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»8N • «T4«-IU1 



THE COMPUTER JOURMAL 

ror Those Who Interface, Build, and Apply Micros 



l»su« Numb«f 22 Jonoory— February, 1 966 S2.30US 

NEW-DOS 

Write Your Own Operating System pages 

Variability In The BDS C Standard Library 

Porting BDS C To CP/M 86 page 21 

The SCSI Interface 

Introductory Column To A Series pageis 

Indexed Sequential Access Method Files 

Using Turbo Pascal ISAM Files page27 



The AMPRO Little Board Column 



The Computer Corner pagese 



page 42 



The Computer Journal / Issue #22 



THE COMPUTER JOURNAL 

190 Sullivan Crossroad 

Columbia Falls, M or) tana 

59912 

406-257-9119 



Edltor/Publlsh9r 

Art Carlson 

Production Assistant 

Judie Overbeek 

Circulation 

Donna Carlson 

Contributing Editors 

Nell Bungard 

C.Thomas Hilton 

Jerry Houston 

Bill KIbler 
Rick Lehrbaum 



The Computer Journal* Is a bimort- 
thiy magazine for those who Interface, 
build, and apply microcomputers. 

The subscription rate is $14 for one 
year (6 Issues), or $24 for two years (12 
Issues) In the U.S. Foreign rates on 
request. 

Entire contents copyright © 1986 by 
The Computer Journal. 

Advertising rates available upon 
request. 

To Indicate a change of address, 
please send your old label and new ad- 
dress. 

Postmaster: Send address changes 
to: The Computer Journal, 190 Sullivan 
Crossroad, Columbia Falls, Montana, 
59912. 

Address all editorial, advertising and 
subscription Inquiries to: The Com- 
puter Journal, 190 Suiilvan Crossroad, 
Columbia Falls, MT 59912. 



Editor's Page 



Restating Our Objectives 

When I started TCJ, I wanted to 
stress the fact that we would not be 
publishing page after page of 
product reviews on the latest 
spreadsheets and appliance-type of- 
fice systems. My intention was to in- 
dicate that we would cover subjects 
of interest to those who had to im- 
plement and interface the systems, 
but not for the end-user who only 
wanted an appUance-type machine 
and who was not interested in the 
how and why of making the com- 
puter work. But, as pointed out in 
Wilkinson's letter in this issue, it 
sounded like we were 0^fLY in- 
terested in measurement and con- 
trol. 

This is definitely NOT the case! 
What we are interested in is under- 
standing the hardware and software 
so that we can make the computer do 
whatever it is that we want it to do. I 
don't want a computer in a sealed 
box with canned programs that does 
something the way some 'experts' 
decided that I should do it. I want to 
tear into it and make it do what I 
want, the way I want to do it. For my 
applications this involves hardware 
construction, programming, and a 
lot of interfacing to physical devices. 
One of the big stumbling blocks has 
been the necessity of working around 
the limitations of an operating 
system— but with Hilton's series 
starting in this issue that problem 
will also be solved. I'll talk more 
about that a little later. 

With this issue we are starting sec- 
tions on the SCSI interface, 
programming in C, writing your own 
operating system, Ampro SBC user's 
support, and continuing the Turbo 
Pascal series with an article on 
ISAM files, plus The Computer Cor- 
ner and other goodies. We have a 
number of excellent articles on hand 
and in progress for future issues, so 
our coverage will expand and im- 
prove. 

Write Your Own Operating System 

As Tom Hilton points out in his let- 
ter, what the user sees is the ap- 



plication program and not the 
operating system. In a well written 
program the user should never see 
the system prompt or have to deal 
with the system— if he does he 
should criticize the program and not 
the system. It is only those of us who 
program and implement systems 
who should have to deal with the 
operating system directly. 

I have had a love/hate relationship 
with CP/M because it does some 
things so well while doing other 
things very poorly. I finally got ZC- 
PR3 running (it came installed on 
the Ampro 122), and it eliminates 
most of CP/M's limitations. But I 
won't be satisfied until I fully under- 
stand exactly what the OS is doing 
and can mocUfy it to do what I want. 
In order to control the computer we 
have to be able to control the OS, and 
Hilton's series on NEW-DOS starting 
in this issue is exactly what I was 
looking for. 



".... SCSI interface pro- 
gramming in C, writing 
your own operating 
system, AMPRO SBC 
user's support ...." 



Even those who use other systems 
should follow the series in order to 
understand what a system 
does— and they can envy CP/M 
users because we can modify our 
system. By the end of the series we 
will be able to write our own OS with 
the features we want, without paying 
any license fees or depending on an 
unresponsive company for support. 
TCJ will organize a user group to 
support NEW-DOS so that we can 
help each other. We realize that 
there are other systems, and MS- 
DOS may be the best choice for some 
uses, but a disk-based OS which we 
can create and modify gives us great 
o[^rtunity to learn and grow. 

(Continued on page 49) 



The (Computer Journal / Issue #22 




Using C 

I read with interest your editorial 
in Issue 21. It is possible to get most 
of the things you wish using some C 
compilers (plus add-ons) but unfor- 
tunately, the BDS C compiler does 
not support them. Many C compilers 
support the pre-processor directives 
#asm and #endasm. The use of these 
directives allows the programmers 
to include in-line assembler code in 
his or her C code. When the pre- 
processor finds these directives, the 
code is marked so that it will not be 
optimized during the optimization 
pass on the compiler (if this pass is 
present). This is a great im- 
provement over the method which 
you have to use with BDS C. In terms 
of "flash compiling", it is my im- 
pression that this could only be done 
using a single pass C compiler (with, 
of course, a built in editor). The 
problem with single pass C com- 
pilers is that they are sensitive to the 
order in which #define's are listed in 
the code. If several #define 
statements refer to each other and 
are incorrectly ordered, a single 
pass compiler could end up with 
unresolved references, which would 
halt compilation. A good alternative 
would be the use of a C interpreter, 
several of which are now on the 
market (although I believe all of 
them are targeted at the IBM PC en- 
vironment, rather than CP ) . These 
generally have built in editors which 
will point back to the source code if 
syntax errors are found (similar to 
Turbo Pascal's editor). They are 
also generally syntactically com- 
patible with major PC C compilers 
(Lattice and Microsoft compilers 
and occasionally some others). The 
problem here is that you are set back 
the price of the interpreter (which 
can range from $100.00 to $500.00) , as 
well as the cost of your compiler 
(which, for Lattice and Microsoft 
are not cheap). 

Don Howes 

Pullman, WA 



Is CP/M Dead? 

Is CP/M dead? Are hammers 
dead? Are nails dead? Is cooked food 
a thing of the past? There are some 
questions we writers should not 
dignify with an answer, and would 
not, if it weren't so much fun ! 

To be quite honest, I never saw 
pure, virgin, CP/M until I just had to 
see what it looked like. Pure CP/M is 
an option on the Ampro Series 100 
systems. When I first booted it, I 
thought my terminal program had 
gone into high orbit (again). The 
point is, who uses pure CP/M? If 
CP/M is dead, then it has been dead 
for a long time, and will be dead for 
decades to come. 

It is only we masochistic system 
programmers who ever see CP/M. 
We are the only ones who appreciate 
it, albeit in a love/hate relationship. 
What the user sees, and com- 
municates with is the Console Com- 
mand Processor, (CPP). While it is 
a part of the standard CP/M Disk 
Operating System, (DOS), it is 
seldom allowed to remain as Digital 
Reseach intended it. Perhaps the 
greatest gift to computerdom was 
Richard Conn's ZCPR, a CPP 
enhancement. 

I began computing in an industrial 
world. The king of the space 
program was the RCA CDP1802 
microprocessor. This was a CMOS 
chip, and has been available literally 
for decades. People are just now 
discovering CMOS technologies, 
though few really understand them. 
Hence, my perspective is that of 
machine intellect, robotics, 
satellites, and deep space probes, 
where the machine must fend for it- 
self. 

My world does not generally in- 
volve spiff y graphics displays, 
though I appreciate that type of 
programming genius. Nor does it 
generally involve complex 
mathematical process. I am, after 
all just a lowly chip mechanic. 

As I entered into the world of con- 
sumer computers I was spellbound 
by all the nifty features of CP/M 
machines. After about an hour I had 



to say to myself, "this is neat, but 
how do I get to the system, and will 
all of this spiff get in my way?" With 
the exception of the Ampro Z-80 
machines, all that spiff did get in the 
way. Ampro allows me, the 
operator/developer, to decide how 
much spiff I want. 

These days I design systems for 
the disabled community. These are 
challenges greater than the space 
program, and demand the highest 
technology. I need a system that I 
can tailor to the specific needs of the 
individual. Not only must I be sure 
that the system may be used by the 
individual with ease, but it must be 
reliable. 

Now then, for the casual operator, 
CP/M does not present a great deal 
of flash, nor pretty noises. It must be 
remembered that CP/M was 
designed as a business workhorse. 
For a person who just operates a 
computer, or perhaps plays with an 
assembler, CP/M type systems have 
little to offer. However, it is this type 
of computerist that is the most vocal 
in what has been termed, "The DOS 
WARS." When running an ap- 
plications program, the operator 
never sees the operating system, 
only the applications program. 
These vocalists are judging the per- 
formance of these programs, not the 
operating systems. But, as I think of 
it, these people do not read TCJ 
either, but dough-files, or BC 
Weekly. 

The best thing about CP/M type 
hardware, as opposed to the CP/M 
operating system, is that there is a 
reasonably standard way of doing 
things. If I didn't have a fully 
debugged set of routines to handle 
the disks, and terminal, I'd have to 
write them. That is just the reality of 
computing. 

In my work I use equipment 
designed to run CP/M. There are a 
number of reasons for this choice. 
First, is the price. Thousands of 
people are maimed daily in 
automobile mishaps. When a 
disability strikes money is an issue. 
In other fields, it is the same con- 



The Computer Journal / Issue #22 



cept. The boss wants the lowest cost 
technology that will do the job. A 
large amount of CP/M hardware is 
unuseable. Were it not for the way 
the Ampro systems allow you to 
modify the operating system, I 
would have designed a similar 
system to run MY operating system ; 
not CP/M, an operating system to do 
a specific task. CP/M is no longer a 
mystery. Those who know hardware 
generate operating systems for 
special tasks. You can't do that with 
the PC clones without new ROMs, 
higher end costs, and complexity. As 
a matter of fact, TCJ will be doing a 
series on how to design your own 
operating system for Z-80 
technologies. Why buy a DOS when 
you can write your own to do what 
you want it to? 

As the American market turns fiu*- 
ther towards the 16, and 32 bit 
technologies, the Japanese will in- 
vade the CP/M world. They may caU 
it something else, but has anyone 
been noticing the number of very low 
cost Japanese CP/M systems on the 
Market? As with most things the 
Japanese will take our left-overs, 
perfect them, and sell them back to 
us. This is like selling an Eskimo 
snowballs. But, they keep on doing it, 
and we keep going for it. Take the 
HD64180 superchip. It is nothing but 
a souped up Z-80. Some say its only 
real advantage is being able to ac- 
cess more memory. Fine, I can live 
whith that easily. 

The bottom line is that, from the 
machine level, or "the other side of 
the screen," as I like to say, there 
just are not systems as easy to work 
with for the price asked. 

Creative Computing published a 
list of "The World's Worst Com- 
puters," in an article by that name. 
The IBM PC headed this list, with 
PC clones coming in second, and the 
IBM PC JR. takii^ third. Comments 
ranged from "user hostile," to "an 
uninspired design..." I happen to 
agree with all of the negative com- 
ments about 16 bit machines, and 
agree with but two positive commen- 
ts: they do crunch numbers, and 
they do have neat graphics. The 
prices being asked for these 
technologies are near criminal. The 
sophistication, for most board level 
projects, is like putting airbrakes on 
a turtle. 

Now what would I want for 



Christmas, had I all the money I 
should want to spend on computers? 
A Sanyo MBC-775, (Japanese por- 
table PC clone), the Borland "Turbo 
Jumbo Pack," and a program to do a 
"school newspaper." Now what 
would I do with this $5000 Christmas 
package? Why develop applications 
for the Ampro Z-80 Little Boards, 
and The Little Board '186! I need a 
compact portable for many personal 
and professional functions, to use as 
a terminal, and a 16 bit machine to 
run the fuU Borland Package. 

Is this hyprcritical, or at best 
treason? I don't think so. Tools are 
tools. My personal, and applications 
programming productivity would be 
increased 4000% with the Borland 
package, especiaUy when applied to 
the Uttle Board '186, if I could afford 
all this. Why a Japanese clone in- 
stead of buying American? The 
Sanyo, in my opinion is a superior 
implement, cheaper than any 
American model, and has a color 
monitor built-in. 

The key concept is that tools are 
tools. For most of my work the Z-80 
systems are the best for the job, and 
of the lowest cost. I can work with 
them. Just by the way they are 
designed, and constructed the IBM 
machines are not all that great for 
board level systems, except for 
building super computers. Their cost 
is nearly double that of the Z-80 
systems. From an applications 
progranmiing perspective, however, 
more is available for the IBM types, 
and I want the full Borland Toolbox 
series. So, on the "operator's side of 
the screen," I'd like the Sanyo Clone, 
for personal and program develop- 
ment. For the mainstay of my work, 
however, I prefer the single board Z- 
80 systems, especially the Ampro 
Little Board. Many clients, knowing 
no better, want the IBM systems, 
just because their neighbor, the used 
car salesman, said his brother-in- 
law's sister's cousin heard they were 
good. The key point is that each are 
tools with specific functions, and 
people who don't really know better 
are demanding systems that are 
IBM compatible. 

Is CP/M dead? Perhaps, but the 
systems that run CP/M, and will 
tolerate a user's version of the DOS 
will be with us for decades to come. 
Is CP/M dead? Who cares, as long as 
the hardware that will run it keeps 



getting cheaper? The only problem 
with hardware that will run CP/M, 
and CP/M itself, is that tht skill level 
of users is dropping, and the desire 
to learn is nonexistent. The popular 
trend is to serve the computer, not to 
have the computer to serve you. 
When viewed in this context, the en- 
tire issue is stupid, in my opinion. 
Tom Hilton 



More on Soldering 

I was reading Mr. O'Connor's ar- 
ticle about soldering in issue #20, and 
I'd like to mention a couple of points 
he missed. It's an exceUent piece, 
with more useful information about 
soldering (and clearer explanations 
of what's going on) than I've ever 
seen in one place before ; but ever so, 
there are a few more details that a 
potential kit builder might find 
useful. 

For example, iron-plated tips for 
the soldering iron— why are they bet- 
ter than plain copperf They're a lot 
more expensive— are they worth it? 
Yes, because they don't have to be 
cleaned, scraped and re-tinned 
nearly as often. In fact, Mr. O'Con- 
nor hardly mentioned tinning the tip 
at all— and that can make a big dif- 
ference in the efficiency of heat 
transfer. 

About flux— first, the name. Mr. 
O'Connor's explanation was ex- 
cellent, but he left out one important 
point: the reason it's called "flux" is 
because it makes the solder flow 
over the surfaces being soldered. 
Soldering flux is primarily a "wet- 
ting agent" for metals. Just as soap 
or detergent helps water to coat and 
cover a surface, instead of clumping 
into little beads and droplets, flux 
helps the solder to make a thin, 
penetrating film over the metals 
being soldered: this improves heat 
transfer during soldering, and 
provides for more and better metal- 
to-metal contact (which means bet- 
ter electrical conduction) . 

Rosi-core solder is very 
useful— but don't sneer at paste or 
liquid rosin fluxes (NOT acid 
fluxes), old-fashioned though they 
may be. For an experiment, try tin- 
ning the end of a piece of stranded 
wire (coating it with solder, to make 
it more manageable before connec- 
ting it to a terminal in a tight place) , 
First the usual way, by simply 



The Computer Journal / Issue #22 



heating the wire and applying rosin 
core solder; then do the same again, 
but put a little paste of liquid flux on 
the wire before you start. You'll find 
that the added flux makes for a 
much neater and quicker job, and 
also requires less heat from the iron. 

Only a teeny tiny bit of flux is 
required (more will just make a 
mess) ; but the difference it makes is 
tremendous! 

One final, but very important 
point: about why (and when) you 
need to clean the flux residue off af- 
terward. They tell you that rosin is 
non-conductive... but that's not quite 
true. It's non-conductive, compared 
to a piece of wire; but compared to a 
ten-megohm resistor, it conducts 
quite nicely, thank you ! 



For instance, if you're trying to get 
a long time delay in a 555 timing cir- 
cuit, by using a fairly small 
capacitor and a very high resistan- 
ce, you had better clean off all the 
flux when you finish— or the conduc- 
tivity of that "non-conducting" flux 
may upset your calculations con- 
siderably. Or if you're working with 
CMOS ICs, you may find that current 
leakage from one of the power suply 
pins to an adjacent input pin, 
through un-removed rosin flux 
residue, can shut down the circuit 
entirely! 

In short, whenever you're working 
with high resistances or low curren- 
ts, you had better clean all the old 
flux off the board before you power it 
up, or you may find a nasty bug in 



your circuit! 
Jock Root 
L.A.,CA 




Z SETS YOU FREE! 



Z Operating System, an S-bit OS that flies) Optimized HO64I80/Z80 assembly language 
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Keai-time control kernel option allows quick software development for industrial control 
applications otner tools and utilities for office desk-top personal computing functions, local area 
■■e^^ork^ to Einemet, AppieTalk Omnmet '\rcNei, PC -Net (Syteki — 'rorr mice to mainframe 
. ; mmand coniro: and communications DisiriDuted processing application programs are easilv 
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• ExtrerTie organizational flexiDtliry eacri directory anotner environment 

• Multiple Commands per line 

• Aliases (complex series of commands known by simple namesl Ann va'.aoie passmg 

• Named Directories with absolute password securii> 

• Full-screen command line editing witn previous command recall and execution 

• Shells and Menu Generators, with shell variables 

• Command-file search Paths, dynamically alterable 

• Screen-oriented file manipulaiion and automatic archiving and backup 

• 512 megabyte Me sizes 8 gigabyte disks handled 

• Auto disk reset ^»vhen changing floppies 

• TCAP database handles characteristics of over 50 computers and terminals 
more easily added 

• Tree-structured online help and dcxumentation subsystem 

• 76 syntax-compaliDle support utilities 

Your missing link has been found — Zl Now fly with eaglesi Fast response, efficient 
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^m • 



Echelon, InC* tOIPirsI street • Suite 427 • Los Altos. CA 94022 • 41S,94»-3820 



FORTH 

Bill Kibler: I have just read your 
Computer Comer column in issue #17 
and I am interested in your idea of 
building a Z-80 FORTH unit. I am 
currently learning 64 FORTH from 
HES on my Commodore 64 and 
would like to put FORTH on a Z-80 
board that I have already built. 

I became interested in FORTH 
because I work with elevators which 
are rapidly becoming computerized 
and FORTH seems perfectly suited 
to this fleld. 

Any columns on Z-80 FORTH 
would be greatly appreciated. As 
usual, you and everyone at The 
Computer Journal are doing a great 
job. 

O.K. 

New York 



Data Acquisition and Control 

I enjoy reading your informative 
journal. Mr Jerry Houston's article 
on analog data acquisition and con- 
trol systems was especially in- 
teresting to me. 

I wonder if he and/or others might 
be interested in elaborating on ac- 
tual applications of ADC units, such 
as those mentioned in his article. As 
you know, some of these devices are 
relatively inexpensive and most can 
be interfaced through RS-232 with a 
number of different micros. In my 
opinion, they present a unique oppor- 
tunity for us who interface micros 
with the real world. I am sure that a 
number of your current readers and 
potential new subscribers would be 
interested in this area. 

Thanks for your efforts on editing 
and publishing The Computer Jour- 
nal. 

Matthew K. Rogoyski, Ph.D. 
Hotchkiss, CO 



( Continued on page 38 ) 



The Computer Journal / Issue #22 



NEW-DOS Write Your Own Operating System 

Part 1: The Console Command Processor 

by C. Thomas Hilton 



We Listen to Our Readers 

A number of professional readers have written to 
request more technically based articles. While these 
readers may be professionals, who use computers in their 
work, they may not always be computer professionals. 
Most often they use their systems to interface an ex- 
periment, or just require more control over their equip- 
ment. 

We have all heard of the "DOS WARS." Of those 
professional computer users who have made comment, 
most have stated that the 16 bit systems "have more 
features." Most however resent the higher cost of 16 bit 
systems. 

The point of issue is not which operating system is the 
best. The user does not communicate with the operating 
system directly, but through a Console Command 
Processor, (CCP), which translates human commands 
into computer based functions. Hence, the number of 
"features" seen is a product of the CCP, not the operating 
system. 

In this series we will be discussing how to modify your 
system to meet your specific needs, or desires. Because 
of their price, and versatility, we will be targeting the 
Ampro LITTLE BOARD* series of Z-80* machines. 
Users of other, or existing, systems may follow these 
discussions and implement the projects. The only project 
series that non-Ampro users will not be able to im- 
plement will be the custom Basic In/Out System, (BIOS), 
which is hardware specific. The BIOS we discuss may, 
however, serve as a model for implementation on non- 
Ampro systems. 

We will open our discussion with the CP/M* type CCP. 
Some users have either purchased the Ampro "FRIEN- 
DLY"* operating environment, or purchased an Ampro 
Series 100 system which has ZCPR3 installed for use. 
Others may have purchased the "Z" System* from 
Echelon. We will term the ZCPR3 systems the "top of the 
line," as far as enhancements are concerned. On the 
other end of the scale is standard CP/M, which is 
available as an option with all Ampro systems. It is with 
the stock CP/M system that we will be^ our discussion. 
In this series we will develop a system whose function is 
mid-way between ZCPR3 and standard CP/M. The best 
part of our system will be that it is ours, not someone 
else's. Our system will require neither extra system 
memory, nor support files on disk for proper functioning. 

The Standard CP/M System - Structure and Terminology 

Figure 1 shows a standard CP/M memory map. (A 
memory map shows where various portions of the system 
are located in memory.) In hexadecimal, ("hex") 
notation, as applied to an 8 bit system, memory locations 
form a four character representation. In hex, memory is 
defined as a series of "lines," and "pages." A line is a 



smgle digit code, or "byte." A "page" of memory con- 
sists of 256 lines of code. The number of lines being 
referenced occupies the two "least significant digits" of 
the hex representation. Hex is read from right to left. The 
number of pages is represented by the left-most two 
digits, or 'most significant" digits. Each pair of digits is 
capable of a single byte value, of 256 elements. Each 
numeric representation begins with the number zero. 



BASIC IN/OUT SYSTEM (BIOS) 


: STANDARD CP/H DISK 0PERATIM6 SYSTEM 


Con«ol» CoM^nd ProcMmor (CCP) 


Tr«n«i«nt Proqrmm iUnmr Proqrmmt 
(D*p«nd«rit IJQon Anount of Mnwiry) 


BIOS and CP/M Hark Af-»«, P*9« Zmro 



FFFFH 
EEMH 



_nv 5y«t» 

_nv Sv«t. 



"V 3y.t. 

D7FFH (End o* n^) 



(Start o4 TPAI 
(Start Of w.i« Yi 



Figure 1 : CP/M memory map. 



Figure 2 shows the basic hexadecimal number system. 
For most people it is easier NOT to attempt to translate 
the hex system into decimal. The key thought is that, in- 
stead of ten fingers, we now have 16 fingers. The number 
system works the same as the more familiar base ten. We 
start at number zero and count to 15, or "F" before star- 
ting a new, left-most number colunm. 



• Ih 

P* 



lln«« or bvt«« 

•quals th« <ir«t tin«. 



or byt* o* p*9« zero 



Th« «tandard h*x 



praqr*«stan i« 



• - a 

1 • ■ 

2 - C 
3-0 
4 - E 

3 - F 



Figure 2: The HEX numbw system. 



This brief introduction to the number system is 
inadequate, but will have to be enough. Supplemental 
reading is suggested for all parts of this series. 

The structure of the operating system is very straight- 
forward when related to the memory map in Figure 1. In 
"the attic," of our microworld, or top of memory, is the 
BIOS. The BIOS is responsible for all hardware depen- 
dent functions. That is to say that the BIOS handles all 
transfer of data, in and out, on a byte by byte, or charac- 
ter by character basis. As the CP/M type operating 
systems may be run on any number of different com- 
puters some means of compatibility was needed. The 
BIOS begins with a 'jump table" to each of its internal 



The Computer Journal / Issue #22 



functions. Each of these functions is implemented in the 
fashion required by the hardware specific to the concer- 
ned computer. We will deal specifically with the BIOS in 
a future portion of this series. 

Underneath the BIOS is the Disk Operating System, or 
'DOS." The DOS may be said to handle the system in a 
form which is system independent. It does not know, nor 
care, what the system specific hardware is, nor looks 
like. All the DOS knows is whom to 'call" to perform a 
specific function. It is dependent upon the BIOS for all of 
its tasks. The BIOS, again, works only in the most 
primitive terms. The DOS, however, works in multiples 
of these primitives to accomplish a task. As an example, 
to print a string of text the DOS sends the string to the 
BIOS a character at a time, who sends each individual 
character to the terminal, or other hardware. To assure 
that a program will run on other computers program- 
mers perform tasks by making function calls, or 
requests, to the DOS, instead of the BIOS. As the DOS is 
the same for all machines, though the bios is not, com- 
patibility between differing systems is had. A program 
may, however, make function requests of the BIOS by 
calling the jump table at the start of the BIOS. The jump 
table must remain in the same relative position for all 
systems. The DOS assumes function addresses to be in a 
given sequence, relative to a given starting address. 

Beneath the DOS is the CCP. It is the job of the CCP to 
interpret the human's commands and perform simple 
tasks with files stored upon a disk. The standard CCP is a 
very simple minded fellow, at best. We will add a number 
of functions to the CCP. Our main focus will be, however, 
to show you how to add your own special commands and 
functions. 

In "the basement" of our system is an area reserved 
for use by the BIOS, DOS, and CCP. This area is the first 
page of memory, and is called, "page zero." We will 
cover the use of this basement area in great detail, but 
later. Finding a place to begin is always the most difficult 
part of starting any project. And, as I often say, no mat- 
ter where I begin, I should have covered something else 
first. With this in mind, let us begin. 

Project Support Disk 

Because many are not familiar with assembly 
language programming, nor the structure of the world on 
the other side of the screen, I have prepared a special 
assembler. This assembler has proven itself to be of 
value to the beginning assembly language programmer. 
We have discussed briefly bytes, lines, pages, and other 
terms. There are even more terms to learn. For example, 
a "word" is a 16 bit address constructed from two bytes. 
The hardest thing for a beginning assembly language 
programmer to understand is where a byte must be used, 
and where a word must be used. This is especially true 
when they are often represented by the same series of 
symbols such as DEFB, DB, DEFW, or DW. In the 
assembler we will be using a byte is called a "BYTE," 
and a word is called a "WORD." I realize this is at best 
treason, to the pundits of tradition, but it is easy to work 
with. 

Additionally, which does one use when representing 
string, or character data? You guessed it, "DATA." The 
common approach to Z-80 system programming is the 



use of the 8080 assembler that came with your system. 
8080 mnemonics have many and varied forms, which are 
confusing at best. We will use a Z-80 assembler for a Z-80 
system, another attack against tradition. Most all of the 
instructions have a simple form, with only two 
variations, a marked improvement. 

This assembler, originally written by Pat Crowe of 
England, is provided for this projectas a user disk. It is 
available from TCJ at a very reasonable cost, as it is a 
public domain program. The source code file can be 
assembled with itself. No other assembler is needed for 
this project. Additionally, all the source code files to do 
all of the projects we will be discussing are provided in 
ready to modify and assemble formats. 

Due to the fact that Ampro distributes the T/MAKER 
system, and bundles it with some system configurations, 
all source code files are presented in T/MAKER format. 
Word Star, and other editors may read these files without 
modification as the files are pure ASCII code. 

Getting Started, (Finally) 

The first thing that we must do is configure a system 
for our use. We do not want all of the spiff and reser- 
vations of memory space used by ZCPR3. Our first 
project will be to install standard CP/M in our systems, 
at the maximum possible memory image. Place a check 
mark in the box provided before each step. This is to 
assure that all steps are performed in the proper sequen- 
ce. 

n 1. Format and SYSGEN a blank disk. 

D 2. Place the following programs on your fresh disk : 

a. M0VCPM.COM 

b. SYSGEN.COM 

c. DDT.COM 

d. CR0WE.COM 

e. CCP.CRW 

f . CCPA.CRW 

g. CCPB.CRW 
h. STATUS.COM 

D 3. Place our working disk in drive 'A' and boot it. 

D 4. Your system should send you to the CP/M com- 
mand line and issue the "A0> " prompt. When the prom- 
pt appears enter: 

A0>MOVCPM61* 

What we have done is told MOVCPM, (do not use the 
ZMOVCPM program), to construct a CP/M system that 
is 61K in size. The "•" tells it to leave this new image in 
memory. 

MOVCPM will, when it has done its work, instruct you 
as to the option to SYSGEN or SAVE the memory image. 
When the prompt reappears enter: 

A0> SAVE 41 MYSYS.COM 

n 5. When the A0> prompt returns, enter: 

A0> SYSGEN MYSYS.COM 



The Computer Journal / Issue #22 



SYSGEN will then ask for a destination drive, enter "A" 
to place the standard CP/M image on drive 'A.' The next 
time SYSGEN asks for a destination drive, answer with 
only a RETURN. 

_ 6. "Flip" the reset button. Your system should come 
back with the prompt: "A>'. Nothing is wrong, that is 
just standard CP/M! 

Z 7. Now enter : 

A > STATUS 

and make note of th? positions reported for the locations 
of the BIOS, DOS, and CCP on the memory map in Figure 
1, if they are different than those shown. 

It is very important to accurately determine the 
location of the CCP. If the new CCP does not begin in the 
same place as the old one, then the system will not fun- 
ction. Each portion assumes another portion to be in a 
given spot relative to itself. 

G 8. If you do not have my source disks and assembler, 
then enter the published source code, and convert the 
data representations to those of your assembler. 

Be sure to set the equate to be used by the ORG 
statement to the proper value in file CCP.CRW, if the 
location of the CCP is other than D800H in your system. 

If you do have the source disks you may now assemble 
the source code by entering : 

A> CROWE CROWE.AAZ 

This will cause the assembler to look for the source file on 
drive 'A,' place the ".HEX" file on drive 'A,' and omit a 
".PRN" file. We do not want a PRN file due to the size of 
the files being assembled. 

n 9. When the source file has been assembled without 
error enter: 

A> DDT MYSYS.COM 

DDT will sign on and present its own prompt, "-', then en- 
ter: 

-ICCP.HEX 
-R3180 

when the "-" prompt returns, enter 

-GO 

which will return you to the "A> " prompt. At this point 
enter: 

A > SAVE 41 NEW.COM 
A> SYSGEN NEW.COM 

and place the new operating system on the 'A' drive as 
was done in step 5, above. Reset the system and the 
command prompt of " A0> " should be returned. 
For a summary of your new system commands enter: 

AO>HELP 

and a help screen will appear. 



A Bit Of Digression 

An Overview of CCP Commands, Old And New 

The standard CP/M CCP has the following commands : 

a. DIR which returns a directory 

b. TYPE which prints a text file 

c. REN which renames a single file 

d. ERA which deletes files 

e. SAVE which we have already used 

f . USER which changes subdirectories 

g. ' P (control-P) which sends whatever is 
sent to the screen to the printer 

h. ^ C which resets the system 
i. S which stops screen display when using 
the TYPE function 

It would be best if you referred to your system manual to 
assure that you understand what these commands are, 
and do. Our new CCP has all of these commands, and 
more, some with expanded functions. The TYPE com- 
mand, which is called "READ," now has a built-in single 
screen paging function. The basic command set is as 
follows: 

a. DIR 
This command functions in the same manner as the stan- 
dard CP/M DIR command. The enhanced variations 
available g^^Q- 

DIR ♦.• S will display files with the "SYSTEM" at- 
tribute 

DIR *.• U will display files of any attribute 

b.READ 
This command functions in the same manner as the stan- 
dard TYPE function, but has a built-in paging routine. 
That is, it will display 22 lines of text from a text file and 
stop, awaiting any keypress by the operator. This paging 
function may be disabled by the suffix "N," for no paging 
enter: 

READ MYFILE.TXT N 

c. LIST 
The LIST function is a relative of the READ command. It 
reads a text file from the disk and sends it to the printer, 
instead of the terminal. No paging options are currently 
available for this command. 

LISTMYFILE.TXT 

d.REN 
The REN, or rename command, renames one file at a 
time, and has the syntax of: 

REN NEW.FIL=OLD.FIL 

where NEW.FIL is the name that OLD.FIL is to be given. 

e.ERA 
ERA deletes files individually, or en masse. Wild-cards 
may be used. If the wild-card of *.* is used the system will 
ask you if you really want to erase the entire directory. 
Forms may include: 



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The Computer Journal / Issue #22 



ERAMYFILE.TXT 

ERAMYFILE* 

ERA MXT 

ERA'.» 

ERA MY????.* 

and so forth. 

f.SAVE 
We have already used the SAVE command. However, 
DDT and the rest of microworld speaks hex. This has 
meant that we have had to translate the number of pages 
to save into decimal to use this command. This function 
now allows the option of specifying the number of pages 
to be saved in a hexadecimal number. 

SAVE 41 MYFILE.COM 
SAVE 12H HISFILE.COM 

To inform the CCP that the number to be worked is in 
hex, the "H" suffix is required. If a file name specified 
already exists the system will ask you if you want to 
overwrite it. 

g. USER 
This command changes the currently assigned "USER 
AREA," or subdirectory. It has the form of: 

USER 12 
USERS 

which would be returned as : 

A12> 
A8> 

in the prompt. The concept of a "USER AREA" is at best 
false, as there are no such "areas" on the disk. All this 
command does is assign special directory numbers. 
Without this ability to assign special directories large 
systems would have many screens of directory listings in 
response to the DIR command. 

h.PATH 
The PATH command modifies the search path the CCP 
uses in attempting to locate a file for us. In the standard 
CCP there is no search path. In this project's CCP the 
system will search the current drive, and current direc- 
tory, then the current drive and the directory assigned by 
the PATH command, (normally zero), then drive 'A' 
current user, then drive 'A' PATH assigned directory 
before complaining that it cannot find the file. The search 
path is not as extensive as ZCPR3's, but doesn't require 
any extra memory or disk support files. 

i.JUMP 
The JUMP command allows the programmer to jump to 
any position in memory and execute a program at that 
location. The syntax for this command is : 

JUMP EEOOH 

All address references are assumed to be in hex. 



The Computer Journal / Issue *22 



j.RUN 
The RUN command will nin any program which is 
currently in memory, without reloading it from disk. 

SYSGENMYSYS.COM 
(exit) 

DIR 

RUN 
(system prompts:) 

Destination Drive? 

k.DO 
The DO function is similar to the RUN command, but 
allows the passing of parameters to the program residing 
in memory. 

STAT 

(exit) 

DO *.♦ $SYS (which sets all files with the 
system attribute) 

l.LOAD 
The load command loads a named file into a given ad- 
dress: 

LOAD 2345H MYFILE.COM 

in which the load address must be in hex, and the file 
must be assembled, or compiled, to run at the address 
specified. 



m. HELP 
The help command displays a user created HELP file, 
one screen at a time. The help file may be created by any 
text editor. The Help file must be named: 

SYS.HLP 

and must take into consideration the paging effect of the 
READ command, which is used to print the HELP file, in 
general use the SYS.HLP file should contain an index of 
other help files. Once this Index is displayed the user may 
enter the command : 



or 



AOREADHELP.ERA 



AOREADST0RY.TXT 



Only the name of the system base help file is predefined. 
The HELP command may also be used in either the cold, 
or warm boot autocommand structure for power-up and 
reset screens or menus. 

n. ^ P, ^ C, and -^ S 
These three control codes operate in the standard man- 
ner. 

We will deal with all of the commands in greater detail 
as we examine the CCP source code. I wanted to give you 
a basic overview of what we will be doing in case you 
wanted to order the source disks before we got too deeply 



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10 



The Computer Journal / Issue #22 



involved. Of course these commands are only those 
which are installed for demonstration purposes. At the 
end of this series you will be able to design your own 
command structures for the work that you do. 

The CCP, A Detailed Look 

The CCP we will be examining has a long and varied 
history. If one had to trace its history it could probably be 
said that the original author was Richard Conn. The ver- 
sion shown here has been assembled from a number of 
"ZCPR" type CCP implements written for four or five 
different assemblers, and untold numbers of machines. 

This CCP, as with all of its forefathers is a public 
domain program. All persons who claim copyrights to 
any given version do so to assure that the program will 
remain in the public domain, and will not be used for 
direct commercial purpose. 

In Figure 3 we begin to look at the source code, as writ- 
ten for the CROWE Z-80 assembler. As with most assem- 
bler files we begin with a long list of equates for terms we 
will be using later in the program. As we progress I will 
excerpt from the source code so we do not have to keep 
turning pages to see what is being discussed. For now, 
make special note of Figure 3. 

Note that the first line of our file holds a line of com- 
ments which are described as T/MAKER Tab Settings. 
The T/Maker editor is, again, suppUed with many Ampro 
systems as the only alternative to the CP/M ED.COM 
program. Many users therefore will not have a copy of 
WordStar or other editor. The target system in this 
discussion is the Ampro Series 100. It therefore makes Ut- 
ile sense to create files with an editor that is not com- 
monly available to Ampro users. A T/Maker file may be 
read by any text editor as it produces a "pure ASCII 
code." This means that there are no flipped bits nor con- 
trol codes hidden in the text file. T/Maker does have a 
quirk, however. There is a 300 character "first line" in 
the text file where tab settings are stored. The maximum 
length a line may assume is 300 characters, in the CP/M 
versions. This tab line gives most languages and assem- 
blers a fit ! When using T/Maker be sure to save your files 
without tabs. This is done by entering: 

WHAT NEXT? NOTABS SAVE 

In the alternative, and what I have done, is use the 
T/MODIFY program to change the default setting of my 
T/Maker system. When asked if tabs should be saved 
with the fUe, answer "NO." The top tab line in our 
program is to set the internal tab settings for assembly 
language programming. All that is required to set these 
tabs is to place the cursor on this tab line and enter : 

ESC 

S 

'^ I or TAB key 

all tabs represented by this model line will be installed in 
the system for as long as the power is on. 



two boolean symbols. A boolean symbol is a logic 
operator which may have either of two states, either 
"true," or "false." A negative logic state is, in this 
program, called "NO," and a positive logic state "YES." 
These boolean elements are used for triggering con- 
ditional assembUes. 

A conditional assembly is a section of program that 
either will be assembled, or will not be assembled, 
depending upon the result of an "IF" evaluation. We have 
a number of conditional assembly sections in this CCP. 
Some commands are considered hazardous in a Remote 
CP/M system, (RPCM), as callers may try to "crash our 
system," causing damage to files, and possibly equip- 
ment. For our personal use we will not inhibit these op- 
tions. 



CR EQU tfUM 

LF EOU «AH 

TAB EOU «9H 

ESC EOU IBH 

CTRt-C EOU eSH 

UBOGT EOU ««H 

UOTLAG EOU «4H 

BDOS EOU «5H 

BIOS EOU «EE««H 

TFCB EOU 5CH 

TSUFF EOU 80H 

TPA EOU ClffffH 



Icharactaf-: carriage rvturn 
(ch«r*ct»*-: lin« f*«<] 
t character-: tab 
tcharmctmr: »»cap« 
Icharactar: control -c 
tcp/« Mara boat addraaa 
luaar nua in high rtytibla, diak 
Ibdoa function call entry pt 
;induatrial bioa location 
Idefault fcb buffer 
Idefault diak t/o buffer 
ibaae of tpa 



In the equates above we assign symbols for frequently 
used codes. The first five equates are for control charac- 
ters we will recognize in the program. It is far easier to 
remember a symbol than the actual numeric codes. The 
next seven equates, starting at "WBOOT" will eventually 
tell the program where to go to perform a function, or 
find data. 



NSIZE 


EOU 


61 


fMVro cp/« • 


etrex.p 


EOU 


•DOMH 


tccp location 


CBBUFF 


EOU 


BI054-&2H 





far *apro svr i •• 1#0 



The equates above give us a picture of what our 
memory map is to look like. Remember that we created a 
memory image of a 61K CP/M system early in our 
discussion. MSIZE equates to the size of the CP/M 
system we created. 

Equate AMPCCP is set to DSOOH, which is where, in 
memory, this program is to begin. Note that there is a 
leading zero in the equate. Any time a hex number begins 
with a letter we have to place a leading zero. If we did not 
do this the assembler would not recognize the hex 
representation as a number, but as some kind of strange 
human symbol. All numbers must look like a number in 
some way. 



RCPM EOU 

NLINE5 EOU 

PGDFLG EOU 

HAXUSR EOU 

SVSFLG EOU 

SOFLG EOU 

DEFUSR EOU 



I set to tru« 1* ccp !■ 4or a BBS syvtwB 

inuaOar o* 1 i n»« on crt scrvwo 

(this flaq r«v«f-««« th« dv^ault tt**mct. 

twaMiMua usvr nuabwr •ccMm«t)l« 

:for dtr coflMaand: I i mt ••v> and *dir 

{for dir co M and: list Vmy* f i I •« ontv 

tdv^aul t uMr nuat>«r *ar com filva 



EOU 
EOU 



icondi t tonal loqic boo 1 van dvc 1 arat ion« 



In the two lines of code above we define the states of 



In the next series of equates, which have been sim- 
plified from many versions of the CCP, we tell the 
program what options we want to use, and what our ter- 
minal "looks like." In that our first version of this CCP 
will be for internal use, we have set the RCPM equate to a 
negative state. That is, we are telling the system that we 
do not want a secure remotely operated CP/M system. 

We then answer questions, in compuspeak, about the 
maximum number of lines on our screen, (24), and the 
symbol we wish to use to disable the page scroll feature. 
TTiese two equates, therefore, relate to the READ com- 
mand of the CCP. 



The Computer Journal / Issue *»22 



11 



, 1 




; 


5 




; ; 


; Tab Settings 


For T/Maker Ed 


itor 










Hermit Software's 








Modi 


f i ed CROME Assemb 1 er 
Source Code File 








<c> 


1985 C. Thomas Hilton 




Primary 










Hard war 


e: Aaipro Series 100, lA CPU | 






(Original Li 


ttle Board) 




Systmi: 


CP/M 2. 


2 








(Ampro 


Standard Version) 1 




Function: A True 


Z-80 


Replacement Console Command Processor To: i 






1. Rest 


ore AUTOCOMMAND Function To Ampro 61K CP/M 1 






2. Enhance Standard CP/M Console Functions 1 




Index: 


CCP.CRW 

CCPA.CRW 

CCPB.CRN 




CROWE Source Code File 
CROWE Chain File 
CROWE Chain File 




LIST 










TITLE 


'Aaipro Custom 


CCP Base File' 


» 


NLIST 








9 

5 

■ 


— 


terminal 


and 


'type' customization equates 


9 

NO 


EQU 









YES 


EQU 


0FFH 




;conditional logic boolean declarations 


CR 


EQU 


0DH 




.character: carriage return 


LF 


EQU 


0AH 




•character: line feed 


TAB 


EQU 


09H 




; character: tab 


ESC 


EQU 


IBH 




; character: escape 


CTRLC 


EQU 


03H 




;character: control-c 


WBOOT 


EQU 


0Vr1 




;cp/m warm boot address 


UDFLA6 


EQU 


04H 




;user num in high nybble, disk in low 


BDOS 


EQU 


05H 




;bdos function call entry pt 


BIOS 


EQU 


0EE00H 




(industrial bios location 


TFCB 


EQU 


STH 




{default fcb buffer 


TBUFF 


EQU 


80H 




; default disk i /o buffer 


TPA 


EQU 


0100H 




;base of tpa 


MSIZE 


EQU 


61 




; ampro cp/m size 


AHPCCP 


EQU 


0I)800H 




;ccp location for ampro series 100 


CBBUFF 


EQU 


BIOS+62H 






RCPH 


EQU 


NO 




;set to true if ccp is for a BBS system 


NLINES 


EQU 


24 




; number of lines on crt screen 


P6DFLB 


EQU 


'N' 




;this flag reverses the default effect 


MAXUSR 


EQU 


IS 




; maximum user number accessable 


SYSFLG 


EQU 


'U' 




;for dir command: list «sy« and «dir 


SOFL6 


EQU 


'S' 




;for dir command: list *sys files only 


DEFUSR 

• 


EQU 







I default user number for com files 


9 
• 


0R6 


AMPTTP 






entry: 


JP 


CCP 




; process potential default command 




JP 


CCPl 




; do not process potential default command 
Figures 



12 



The Computer Journal / Issue #22 



The MAXUSR equate identifies the legal number of 
user areas the operator may request in a USER com- 
mand. The number of user areas in most systems is 16, 
due to the way that user areas are defined in low 
memory. Location 0004 contains a single byte which teUs 
us what disk drive we are on, and what the current user 
number is The format for this data is ; 



FIH 



which would indicate that the system was in user area 15, 
(remember that hex starts with the number zero which is 
a valid number) , and drive 'B' was the currently selected 
drive. 

SYSFLG and SOFLG are options to display files of all 
attributes, or system files. When given the "SYS," or 
system attribute, the file will be displayed in a normal 
directory listing. 

The DEFUSR equate is the number which is to be con- 
sidered the default user, or directory number to be used 
in a directory search for an operator specified file. This 
value may be modified, once the system is running, by 
the PATH command. 



ORG 



AMPCCP 



Our ORG statement is set to the value we assigned to 
the AMPCCP symbol, which is D800H. In a larger 
program we could present a number of different values to 
the ORG statement by use of a conditional assembly. 



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AMPCCP 



AMPCCP 



IF 
EQU 

ENDIF 



KAYPRO 
GEOOOH 



IF AMPRO 

EQU OD8000H 

ENDIF 



A standard CCP has two entry points. The ORG 
statement defines where the program actually begins as 
the equate statements have no real meaning to the com- 
puter. Equates are just there to make life easier for us 
humans. Ampro chose not to use the standard means of 
entry into the CCP. This is primarily because their BIOS 
does not check to see if there is a valid cold boot, or 
"autocommand," installed in the position set aside for it. 
The Ampro BIOS assumes that the CCP, or other 
program will take care of this matter. In a normal 
system such a check would be made. If no command was 
noted for execution upon restart the BIOS would jump to 
location ENTRY -I- 3. In this way no time would be wasted 
in determining whether to process this command. Ad- 
ditionally determinations must be made as to when to 
execute such a command. 

This failure to check for the actual presence of a restart 
command causes the Ampro to always enter the CCP at 
ENTRY, or D800. We will retain this dual entry feature as 
other programs may try to use it, being written to be nm 
on a standard CP/M machine. Again, this failure to check 
for a restart command is why the "autocommand" 
feature is lost in the Ampro machines when ZCJPR3 is not 
being used. ZCPR3 makes these determinations. We will 
perform a test for a restart conmiand ourselves, while 
allowing standard CCP entry points. 

To summarize, most systems would enter the CCP at 
ENTRY -f 3 if they had no intention of processing a restart 
command. They would enter the CCP at ENTRY if they 
did want to supply a restart command to the CCP for 
processing. Ampro systems always enter at the ENTRY 
location, whether there is a restart command stored in 
the BIOS or not. We will have to make up for this over- 
sight in BIOS design to allow the use of the standard Am- 
pro "autocommand," while retaining compatibility with 
other CP/M systems. 



CCP 
CCPl 



t pr-oc»ms potential dvfault 

; do not proc*«« potential d*4«ult 



As is noted, the two different entry points are met with 
unconditional jumps to routines that either will process a 
restart command, or will not attempt to process a restart 
command. 

Kindly note that our discussion does not follow the 
physical layout of the source code listing, but rather the 
logical path of program execution. That is to say that 
while we will now discuss the routine "CCP" it is not the 
next entry in the program listing. 



ccp «t«rting point* 

*t«rt ccp and don't proc»«« dv^Ault c o aaartd mtorad 
CCPi: XOR A (••« no dv^ault co—a 



LD 



(CBUFF>,ft 



From our previous discussion we leam that if the Am- 
pro BIOS did its own check for a restart command, and 



The Computer Journal / Issue #22 



13 



ccp starting points 

start ccp and don't process default contaand stored 



CCPl: 



CCP: 



NLOG: 



CBPROC: 



XOR 


A 


LD 


(CBUFF),A 


ccp and 


possibly p 


LD 


SP, STACK 


PUSH 


BC 


LD 


A,C 


RRA 




RRA 




RRA 




RRA 




AND 


0FH 


LD 


E,A 


CALL 


SETUSR 


CALL 


RESET 


POP 


BC 


LD 


A,C 


AND 


0FH 


LD 


<TDRIVE),A 


JR 


Z,NLOG 


CALL 


L06IN 


LD 


A, (CBBUFF) 


OR 


A 


JR 


NZ, CBPROC 


LD 


A, (CBUFF) 


OR 


A 


JP 


NZ,RS1 


JR 


RESTRT 


LD 


BC,9 


LD 


HL, CBBUFF 


LD 


DE, CBUFF 


LDIR 




XOR 


A 


LD 


(CBBUFF), A 


JP 


RSI 



!set no de-fault coounand 



> de-fault coanand 

; reset stack 

5c=user/disk nuaber <see loc 4) 
; extract user number 



»set user nuiaber 

5 reset disk system 

;c=user/disk number (see loc 4) 

;extract default disk drive 

;set it 

;skip i-f 0. ..already logged 

;log in de-fault disk 

;is there system command to execute? 

;if not zero there is a command 



Figure 4 



found that there was none to execute, we would have en- 
tered the CCP at ENTRY-l-3. At ENTRY+3 we would 
have been ordered to jump to CCPl, which is the entry 
point when we do not want to process a restart command, 
or there is none to execute. Both circumstances have the 
same meaning. 

When a command is entered at the prompt, it uses 
BDOS function 10, or input a line of text from the logical 
console device. This function call requires that a buffer 
be defined, and that the first character in the buffer tell 
the DOS what the maximum number of characters to ac- 
cept should be. Function 10 will return to the caller when 
either this number of characters is reached, or the 
operator signals the end of a line by pressing the 
RETURN key, or control-M, ( ^ M) . 



represents the maximum length of the input command 
line. This could have just as easily been stated as : 



MBUFF: BYTE 



80 



With this byte as the first byte in our input buffer we tell 
DOS function 10 to look here for the maximum number of 
characters by saying : 



LD D€. MBUFF 

LD Etc. 1^ 
CALL «M5H 



; 1 Odd th» «ddr««s o^ buffer in OC 
: 1 D«d function nuaAvr into BC p«ir 
iMAt* th« DOS CAl 1 by juapinq tnra 
; location S. paqs 



5UFLEN 


EQU 


90 




MBUFF: 


BYTE 


&UFLEN 




C&UFF; 


EtvrE 







C I BUFF : 


DATA 






CieuF: 


BYTE 


ti' 






RSRV 


&UFLEN- 


(t-CIBUFF 



MaxiMUMi ttuiiwr ivngth 

fltd^: 1 «uM biiffvr lanqth 

nuMbvr of v«lid ct\»r»ctmr% in 

dvfaul t <col d boot ) co«a«nd 

ccMMiAnd «trinq t»f-«in«teir 

*l : total IS 'buf l»n' byt* 



A type of buffer for DOS function 10 is shown above, and 
is from our CCP. The equate BUFLEN states that the 
byte stored in the BYTE at MBUFF should be 80, which 



When DOS function 10 has done its job, returning only 
when the maximum number of characters has been in- 
put, (80), or the operator enters a Carriage Return, (CR), 
it will place the actual number of characters input in the 
byte at location CBUFF. For entry into the CCP at CCPl 
this byte, which contains the actual number of characters 
in the returned command line is our focal point : 

: %t«rt ccp 4nd don' C proc*«s d»f «ult r n— inn 

CCPl: tOR A ;«»t no d«4«ult co^mtmi 

LD (CBUFFi .A 

In this application of the exclusive OR logic function we 
are exclusive ORing the 'A' register with itself, which 



14 



The Computer Journal / Issue #22 



produces a zero figure. Any time a value is exclusive ored 
with itself a zero amount is returned. We could also have 
said: 

LD A,0 

with the same result. Our next instruction states that we 
are to place this zero value into the byte at CBUFF. When 
we leave this instruction, a zero value will be in the byte 
at CBUFF. Why did we do this? Well, the quickest way to 
determine whether there are any characters in the com- 
mand line is to check and see how many characters DOS 
function 10 says should be in the command line. Now if we 
put a zero value in CBUFF, whose function is to hold the 
number of characters in the command line, then when we 
check we will be told the command line is empty. If the 
command line is empty, as CBUFF tells us, then there is 
no use trying to execute whatever is in the conunand line. 
It is empty. Computer psychology at work friends, if you 
can't dazzle them with your brilliance, dazzle them with 
yourbulls#$t. 

Having gone 50 miles in a two line program segment we 
then drop into CCP, where we would have come if we 
wanted to execute a restart command. Yup, now we are 
at where we didn't want to go anyway, and took a two 
liner "short cut" to get there. Oh well, that's high-tech. 



LD 


A,C 


;c-u»«r /disk 


RRA 




;«xtr«ct u%m 


RRA 






PtRA 






RRA 






AND 


eFM 





What we have done is shift the user number bits four 
places to the right, so they are now the four least 
significant bits: 



ecfore: 


UUUUDDOD 


RRA 


LXJF<IN6: 


KUUUUDDD 


RRA 




XXUUUUOD 


RRA 




XXXUUUUD 


RRA 


AFTER: 


XXXXLXiUU 





where X means don't really care. We now do a logical 
AND with the lower four bits, which house the user area 
code, which has the effect of making all the X marks zero 
values. 



Now we move the value of the disk/user byte, which now 
only has the user number, into the 'E' register from the 
accumulator, or 'A' register. We make this move in 
preparation of calling a subroutine to deal with the user 
number. 



CM-L 



;r» » at disk vyst** 



I start ccp and po«stblv procv 



LO 
PUSH 



■ dv^ault c 
trwmmt *tack 



lc^4aar/dt«k 
l«xtract u««r 



Having arrived here we have to explain some assum- 
ptions we have made and thus far ignored. The first of 
these is that the BIOS is supposed to place the current 
disk and user area in the 'C register before jumping to 
the CCP. 

However, the first thing we do when we actually get in- 
to the CCP is create our own STACK. A stack is a place 
where you stuff things just to get them out of the way, 
such as the place to return to after a subroutine CALXi 
and data you want to in^serve. A stack builds down, and 
you "PUSH" things onto it, and 'POP" things off of it. In 
our CCP we have memory reserved for these stack fun- 
ctions called, of course "STACK." The register 'SP," into 
which this 16 bit value is loaded is used 1^ the processor 
as well. Having defined where our closet of values is, 
where to stuff things, we immediately stuff the disk data 
sent to us in the 'C renter for safekeeping. 

Now remember when we were talking about USER 
areas a while ago. No? Well go back and look, I'll wait, I 
mean I've nothkig better to do than wait on you, just so I 
can confuse the 'ell out of you again, so go ahead... go 
back and reread that section I'll wait 

I am assuming that you now know that the user area 
number is held in the upper portion of the disk/user byte 
at location four. Now if a byte is eight bits, Uien Uie upper 
four bits reiMresent our user area. We first move the 
disk/user byte into tiie 'A' register, from Uie 'C register 
and then use the command Rotate Right Accumulator, 
(the 'A' register) , to extract Uie user number. 



These two calls set the user number and disk number, 
which we received from the BIOS, into the storage area 
at 0004H and reset the disk system so that everything is at 
a starting point for further operations. This setting things 
up is called "initializing the system." 

We then do almost the same thing, separating the disk 
number now from the user number. First we get the 
original value from off of the stack, put it in 'A,' and then 
do a logical and on the lower four bits. This is essentially 
the same way we did the user value except that the value 
we want is already in the lower four bit position. 



LD 


A.C 


lc-u«OT-/dtmfc rnj^MT- tmmm lei 


HMO 


•FM 


l»tr>ct d^ault tttmk *-tv« 


u> 


(TntlVEI.A 


t«M it 


Jll 


2.ia.ae 


IKkip If •...already loQgad 


C«LL 


LOSIN 


Hog in i>*«ault disk 



Now it could be that the system drive, disk 'A,' whose 
number is zero, is already assigned. The action of AN- 
Ding out drive value would set the 'Z' or Zero Result flag 
if it was. The system, or default drive will always be the 
lowest drive number. If this is in fact what has happened, 
that the drive number is already zero, then we do not 
have to log in the system drive. If the value isn't zero then 
we have to assign the new drive, or 'log it in. ' 

Now then, remember all the discussion about the 
restart conmiand? We have to deal with the possible oc- 
curence of a restart command now. From our discussion 
above, can you determine how we will deal with this 
determination? 



LO 


*, <CnUFFI 


lis thmrm av«ta« i ii^Miil 


OR 


« 




JR 


HZ.CVROC 


tif not laro th«r» i« a c 


LD 


*. (CMTFI 




am 


* 




JP 


NZ.RSl 




JR 


RESTRT 





The Ampro "autocommand" or restart conunand is 
located 62h bytes above the BIOS eatiy point. Just like 



The Computer Journal / Issue #22 



IS 



CBUFF it has a value of actual characters in the restart 
command line. Ampro has limited this amount to just 
eight characters. At NOLOG we sneak a peek at the byte 
which is to tell us how many characters are in the restart 
command. We load the accumulator, or 'A' register, with 
that value. We then do a logical OR with the accumulator, 
or OR it against itself. We do this to see if there is a zero 
value in it. If there is then the 'Z' flag will be set after the 
OR function. 

If the 'Z' flag is not set then the value was not zero and 
we want to jump relative to where we are, upon a nonzero 
returned value, to the location represented by CBPROC. 
"CBBUFF" means "cold boot buffer," and "CBPROC" 
refers to cold boot processing. 

Now if there is a zero value in the BIOS restart com- 
mand buffer, (CBBUFF), we check to see if there is a 
command in CBUFF, which is the CCP command buffer. 
If there is a command in this buffer then we will jump to 
RSI, else we will jump to RESTRT for normal CCP 
processing. 

It is important to note that we are checking two restart 
buffers, why? Well, in my system you can have a com- 
mand in the cold boot buffer and a command in what I 
call the warm boot buffer. The BIOS is loaded from disk 
only upon a power-up or reset condition. The CCP is 
loaded upon every warm boot. In this way it is possible to 
configure the system, using either or both restart com- 
mand potentials, to assure that the system never reaches 
the command line. That is to say that even if the power 
goes off the system can recover and reset itself. This is 
important where reliability is at issue. 

From this point we again have a fork in the processing 
road. If there was a cold boot command lurking in CB- 
BUFF then we have to discuss its processing. If there was 
a command in CBUFF then we have to discuss it, and 
then discuss what to do if there were no restart comman- 
ds at all to deal with. Let us begin where we jumped off to 
do the cold boot command, which would have sent us to 
CBPROC. 



.CBBUFF 
, CBUFF 



CBPROC 


LD 


BC.9 




LD 


ML. CBBUFF 




LD 


oe. CBUFF 




LDIR 






XOR 


A 




LD 


(CBBUFF) ,A 




JP 


RSI 



At CBPROC we perform a transfer of the restart com- 
mand string from CBBUFF down into CBUFF. We do 
this by using a Z-80 specific assembler code, "LOIR." We 
know that the Ampro "autocommand" in the BIOS allows 
only an eight character file name. We also know that, like 
the CBUFF format, it has a number which indicates how 
many characters are in the command line.In the LDIR 
instruction the 'BC register pair, (think of them as the 
"byte counter"), is loaded with the maximum number of 
characters we want to move. In this case the number of 
characters is nine. The actual BIOS autoconmiand buffer 
looks like this: 



ORG B10S-^62H 
BYTE • 
DATA 
BYTE 

af«5 AUTOCHO*l» 



;nua*^«r of ch«ract*f'« in coai 

;bl«nk co w and fil* n^mm 

; tvf-Minat inq null ch*r*ct»f- 



We next load the 'HL' pair with the source address of the 
data we want to move, CBBUFF. We cannot use the 
AUTOCMD label as it is unique to the BIOS source code. 
We could have used it here as we had defined it with the 
value of EE62H instead of using CBBUFF. But, we are 
concerned with the Cold Boot BUFFer. The 'DE' register 
pair is used to specify the DEstination address for our 
move. The destination address is CBUFF. CBUFF is 
used for all command processes in our CCP. 

Having defined the number of bytes to be moved, by 
placing this number into the 'BC register pair, the source 
address of the nine bytes to be moved in the 'HL' pair, 
and the destination of these bytes in the 'DE' pair, we are 
ready to make the move. The move is made by uttering 
the magical incantation "LDIR." (Hey! Give me a 
break! After all that set up such an anticlimactic ending 
needs something. OK, so it isn't magic. I bet you are the 
type that pulls back the Wizard of Oz's curtains just to 
ruin the show!) 



(CSBOFF) 
RSI 



So, party poopers and all, the move has been made, and 
the command hidden away in the BIOS is now in CBUFF, 
complete with the number of characters in the line. We 
now zero the accumulator with the exclusive or com- 
mand, and stuff the zero value into CBBUFF, where we 
just moved our restart command from. 



In this case we are ignoring the terminating null as we 
know how many characters there are we want to move. 



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16 



The Computer Journal / Issue #22 



Now why did we do that after we just went to so much 
trouble to move it down where we could worlc on it? 
Remember that the standard Ampro BIOS does not per- 
form its own check for a restart command in the 
AUT(X;MD slot. Because it does not do this checking it- 
self it does not make the decision as to jump into the CCP 
at ENTRY, or ENTRY -1-3; "to process or not to process, 
that is the question." The Ampro BIOS always jumps into 
the CCP at ENTRY, which is the process a restart com- 
mand. 

The BIOS is loaded from disk only from a power on or 
reset. Yet it loads the CCP back into memory after every 
warm boot function. A warm boot may be executed after 
a program is run, or when we press control-C. Now if the 
Bios always jumps into the CCP at ENTRY, to process a 
restart command, our restart command will be detected 
and executed every time the CCP is entered. 

The object of the CBBUFF processing is to execute a 
restart command only once, and that is only upon power- 
up or reset. To prohibit re-execution, called "reentry," 
we put a zero value in CBBUFF. The next time we come 
through and check this position we will be told that there 
is no restart command in the BIOS, hence we will not try 
to process it. 

Having zeroed out the BIOS restart command we jump 
to RSI where a normal command in CBUFF, the CCP 
restart conmiand buffer, is processed. Before we go to 
that routine, however, let's keep in mind what we have 
just done with the BIOS restart command and examine 
the normal CCP restart functioning. 
I heard thatl Someone said, "why don't we just change 
the Ampro BIOS so it doesn't create all these problems 
with a simple restart command?" Well, Ampro had a 
reason for doing a direct ENTRY jump into the CCP. In 
the interests of compatibility we don't want to upset 
thing s anymore than we have to. When we do our in- 
dustrial BIOS this is an option we may explore. But let's 
not get ahead of ourselves. For now this is the way we 
have to do things. 

Let's review for a moment. At NOLOG we made a 
determinationas to whether there was a restart com- 
mand in the BIOS. Review the code provided below. 



LD 


A, <CB8UFF 


OR 


A 


JR 


Nz.cmtoc 


UD 


A, ICaUFFI 


OR 


A 


JP 


NZ.RSI 


JR 


RESTRT 



II* thOT-a »v«t»« co«iMnd to •K«cot«-> 
li* not xmro tttmrm i« • commanti 



If there was a restart command in the BIOS we would 
have jumped to CBPROC, which we just finished 
discussing. At CBPROC we moved the command from 
the BIOS into CBUFF, in the CCP, and jumped to RSI. 
Let us now assume that there was no command in the 
BIOS to be processed. In this case we drop into the code 
that makes a check to see if there is a command in 
CBUFF. 



LO 
OR 

JP 



We do the same thing as we did for CBBUFF, that is 
check the byte holding the number of characters in the 
text string. If it is a zero then there is no command to 
process. A nonzero value indicates that there are charac- 



ters present, a command to execute. At this point we 
would jump, if there were a command, to RSI, where all 
roads for execution of a command lead. 

Now remember that I said that the CCP is reloaded af- 
ter every warm boot, and the BIOS generally only once 
per session? Now if we placed a command Une in 
CBUFF, the CCP command line, and wrote it to disk, 
then every time the CCP was loaded it would execute our 
command, wouldn't it? Yes it would. The first thing we 
check is to see if there is an initial restart command in the 
BIOS. If there is we move it into the CCP and execute it, 
over-writing any command that may currently be in 
CBUFF. Once we move the BIOS restart command, 
however, we zero out the character byte so we do not re- 
execute that conunand. But, every time the CCP is 
reloaded, had we a command written into the CBUFF 
conunand line in the CCP it would be executed after 
every warm boot. It would be impossible for the system 
to ever reach the "A0> " prompt as it would always take 
a priority command from the restart procedures. 

Our priority for automation of our system could be 
stated as: 

BIOS AUTOCOMMAND: Executed Once, Set By 
AmproCONFIG.COM 

CCP RESTART COMMAND : Executed after every 
possible pn^amtermination except a reset or power 
loss. Set by a user program or DDT 

It is clear that we could produce a system that was ex- 
tremely reliable and able to reset itself after an interrup- 
tion of power or other fatal error, as well as restart itself 
after program termination or process sequence. We are 
well on the road to a totally automated system that is both 
reliable, and intelligent. 

Now then, if no restart commands are detected, (all 
roads lead to RSI eventually), then we must get a com- 
mand from the human. This is done by a jump over CB- 
PROC to RESTART, where all CCP roads return. 



u««r 


and tnfMit cammmmt linm tram hi 


LO 


9P, STACK Irwmmt atack 


lOR 


A 


LO 


<CBliFF),A 



RESTRT is the CCP's internal restart point. When all 
internal functions have been completed the CCP will 
return here to begin a new sequence. This sequence is a 
simide procedure of getting your conunand from the 
command line, (M-ocessing the conmiand, if it is an inter- 
nal function, or loading the file you specify, and tran- 
sferring control of the system to that program. 

When we entered the CCP at CCP we set up a local 
stack, and repeat that process again hare, why? Because 
the stack is kept small, and the i»roces8ing of any restart 
command is a sequence all of its own. When we reach this 
point we are in the "inner sanctum" of the CCP where we 
start anew. We set i^) a new stack, (actually we just reset 
the old one as if it were new, and clear our character byte 
at CBUFF). In this way we have a fresh stack and tell 
anyone who may ask that there are no commands to 
execute, everything that needs to be done has been done. 
We may now begin a new day. 



The Computer Journal / Issue #22 



17 



prompt user and input command line from him 



restrt: 



LD 
XOR 

LD 



SP, STACK 
A 
(CBUFF) ,A 



print prompt (du>) 



CALL 


CRLF 


CALL 


GETDRV 


ADD 


A, 'A' 


CALL 


CONOUT 


CALL 


BETUSR 


CP 


10 


JR 


C,RS00 


SUB 


10 


PUSH 


AF 


LD 


A, ' 1' 


CALL 


CONOUT 


POP 


AF 


ADD 


A, '0' 


CALL 


CONOUT 



RS00: 

5 

; read input line -from user 

» 

RS000: CALL REDBUF 

process input line 



RSI: 



CALL 



CNVBUF 



CALL 


DEFDHA 


CALL 


SETDRV 


LD 


<TDRIVE),A 


CALL 


SCANER 


CALL 


NZ, ERROR 


LD 


DE.RSTCCP 


PUSH 


DE 


LD 


A, (TEMPDR) 


OR 


A 


JP 


NZ,COM 


CALL 


CHDSER 


JP 


Nz.con 


LD 


A, <HL) 


INC 


HL 


LD 


H, (HL) 


LD 


L,A 


JP 


(HL) 



; reset stack 



;print prompt 

; current drive is part o-f prompt 

;convert to ascii a-p 

;get user number 
;user < 10? 

; subtract 10 from it 

{save it 

;output 10's digit 



; output I's digit (convert to ascii) 



I input command line from user 



{capitalize command line, place ending 0, 

; and set cibptr value 

;set tbuff to dma address 

{get default drive number 

{set it 

{parse command name from command line 

{error if command name contains a '?' 

{put return address of command 

{on the stack 

{is command of form 'd: command'? 

{nz=yes 

{ i m mediately 

{scan for ccp-resident command 

{not ccp-resident 

{found it: get low order part 

{get high-order part 

{store high 

{store loM 

{execute ccp routine 



entry point for restarting ccp and logging in default drive 



rstccp: 



XOR 

LD 

CALL 



(CBUFF), A 
DL06IN 



{log in default drive 

entry point for restarting ccp without logging in default drive 

RCCPNL: CALL SCANER {extract next token from ct 

{get first char of token 
{any char? 



CALL 


SCANER 


LD 


A, (FCBFN) 


SUB 


y P 


LD 


HL, TEMPDR 


OR 


(HL) 


JP 


NZ, ERROR 


JP 


RESTRT 



and 1 i n* 



Figures 



18 



The Computer Journal / Issue #22 



I print pro 



CALL 


CRLF 


Iprlnt proapt 


CALL 


8ETDRV 


lcuf-r«ot dr-iv* is part o4 


ADD 


A, 'A' 


Iconvsrt to «»cii a-p 


CALL 


CONOUT 





If there was a restart command we would have jumped 
over this program segment. We are assuming that we 
want to get a command from the human operator. Com- 
puters are so willing to please 

The first thing we do is clear a line on the terminal, (our 
ego demands a clear work space) . We clear a line by sen- 
ding a RETURN, (CR, which sets the cursor to the begin- 
ning of a line), and a LINE FEED, (LF, which moves the 
cursor down a line) , to the terminal. To make life easy for 
the human we include a LF every time he, or she, presses 
the RETURN key. 

In the interest of brevity, as we are running out of space 
for this issue we will highlight what each subroutine does. 
We will discuss the various support routines in detail 
later. This time I only want you to understand the 
primary CCP function loop. 

GETDRV returns the binary number of the current 
disk drive. We then add the value of a capital "A" 
character, (41H) to convert the disk drive number into a 
value that can be printed by the terminal. If the disk 
drive number is "0," then when we add the number for a 
capital "A" we have the value of the ASCII code for "A," 
as we have added nothing to it. If the drive number was a 
"1" for drive "B" then the base figure of 41H would have 
one added to it, which would be the code for "B," and so 
on. A standard CP/M system can have up to 16 disk 
drives, represented by the letters "A" through "P.* 

At the assembler level, and unlike BASIC, just because 
we print something doesn't mean a CR/LF sequence is 
also printed. With the printable value of the current disk 
drive in the accumulator we call the subroutine CONOUT 
which sends our character to the terminal. At this point in 
time just the letter is printed. We process so fast, 
however, that when the prompt is printed it appears as if 
the entire prompt appears at once. 



SUB 

PUSH 
LO 
COLL 
POP 

Ksee: ADD 

CALL 



( q»t usar- numbmr 
lu%rr < Ign 

;mubtract 10 from i 

I %MVW 1 t 

(output l«'m diqit 



toutput I'm digit (convart to amci 



In a similar manner we call a routine that returns only 
the current user number. For a hint at how this is done, 
basically, refer to our discussion of the entry point CCP 
early in this article. 

What follows is a simple binary to decimal conversion 
routine. We may not just use an offset value to convert 
the user number into a printable form, as we did for the 
drive number, as the user area is represented as a 
decimal number, instead of a letter. Additionally, we 
have more than one digit to deal with. If the number is 
less than 10 we do not have to formulate the "tens" value, 
which must be printed first. (In the number 10 the "1" is 
the tens value.) 

If the number is greater than 10, then we subtract ten 
from it, which wiU leave us with the "ones" value as the 
remainder. This remainder will be left in the ac- 
cumulator, or 'A' register. As the ones value must be 



printed after the tens value, we will save this remainder 
on the stack. 

LD A,'r ;output lO's digit 

CALL CONOUT 

POP AF 

Having saved the ones value, and because we know that 
the maximum number of drives can never be more than 
16, we just print the character "1" on the screen any time 
the user area is greater than 10. Having the prompt now 
appearing as "Al " we must print the remainder, or ones 
value. So let's get it back, by popping it off the stack, and 
make it printable by adding the lowest possible number 
code to it. The ones value is converted into printable form 
in the same manner as the disk number, except that the 
offset is now the character "0." 



RSOO: 



ADD 



A.'O' 



-.output I's digit 
; (convert to ascii) 
CALL CONOUT 

Note that if the value of the user number was deter- 
mined to be less than 10 we would have come here and 
made this single digit conversion. 



id 1 in« fro 



Because we are assuming that there were neither a 
restart command in the BIOS, or in the CCP buffer, to 
execute, we just have to have a command to process. We 
have printed the "AO " portion of the prompt on the 
screen. REDBUFF supplies the ">" portion of the 
prompt while it waits for our input. This uses the same 
DOS function 10 sequence we have already discussed. 
The buffer for this input is at MBUFF, whose byte con- 
tains the maximum number of characters to be accepted 
from the console. When this number of characters has 
been received, or a CR is entered by the operator, the 
number of characters actually in the conmiand is placed 
in CBUFF. The characters themselves begin at CIBUFF. 

Now then, whether we had a command in the BIOS, one 
in CBUFF when we entered the CCP, or we just received 
one from the operator, our varied paths gather at RSI. 



t proc»«s input 1 i nw 



tcApit«liz« coanaod li 
i and %mt ctbptr valu* 



plmcm andinq •, 



The first thing we do to our command is convert all 
characters into uppercase format. In this way the 
operator can enter command either in upper, or lower 
case. We also set a pointer, CIBPTR to point to the first 
character in our command. We are now ready to get to 
work, after a little bit of preparation. 



tm«t tbuf« to dM« addr»«s 



The first step in preparation is to set up a buffer for any 
and all data from the disk, or terminal. 



CALL 8ETDRV 

LD (TDRIVE),A 



tg«t default driv* m 
l««t 1 t 



Then we save the value of the drive we are currently on, 
so we can **remember*' where to return after we perform 
the command to be executed. 



CALL SCM4ER 

CALL NZ,ERWOR 



I p ar m* c oaM«nd 
twrrar |4 cammmi 



1 1 rm 
contain* a ' "*' 



The Computer Journal / Issue 4'22 



19 



All commands must conform to a very standard format 
for primitive interpreters. This is the format of VERB - 
OBJECT OF VERB. SCANER, we may assume for the 
moment, does a quick syntax check to assure that all 
commands are properly formed. It checks to see if there 
is a disk drive specifier, ( if the command is to be found on 
a different drive), and assures that the user isn't trying to 
do something outrageous. If all is well SCA^fER returns 
with the 'Z' flag set. If there is an error, or an object ap- 
pears before the verb, the 'Z' flag is not set, and we are 
routed to an error handling routine. 



t put return «ddr««« of 
;on th» st«ck 



When we "CALL" a subroutine, the "way home" to the 
caller is placed on the stack. When a RET command is 
seen the top two values on the stack are assembled into a 
16 bit address, and the processor executes a jump to that 
assembled address. The CCP also has to be able to find its 
way home so it can accept another command from us; 
this is, after all, its function in life. Internal commands 
are also called as subroutines, and have to find their way 
home. In the code above we set the return address on the 
stack so that when a RET command is encountered 
program control is sent to a recovery routine. 



A. (TEW>D«) 



ccMMiand o^ torm ' d:cnwnd' "^ 



SCANER will set TEMPDR, (TEMPorary command 
DRive), if the command, or verb to be executed is 
specified to be on another disk drive. To avoid needless 



processing, we can check for another drive assignment, 
and assume that the verb portion of the command is a file 
name. If the value of TEMPDR is other than the system 
drive, drive '0,' then we jump directly to the COM file 
load and execution routines. 



CMDS€R 
n; .com 



r««) dvnt 



If we do not get a clue as to what type of command it may 
be, then we must check to see if the verb is an internal 
command. CMDSER, (CoMmanD SEaRch), will search 
a table of key words, or verbs for a match with the verb in 
the command. This table is constructed as follows : 

DATA 'COMMA^fD' 
WORD COMMAND 
DATA ANOTHER' 
WORD ANOTHER 

The DATA contains the literal verb string. The WORD is 
a label representing the address of the concerned routine. 
Remember that a binary WORD is a 16 bit value which, in 
this case, represents an address in memory. If a match is 
found between the command verb and a verb string in the 
command table, the end of the character by character 
match will be the last verb character, plus one, (as if 
looking for another character to match). Hence, on 
return, if a matching verb was found, the 'HL' pair will be 
pointing at the first byte of the address of the verb's ac- 
tion routine. If no match is found then the command verb 
is assumed to be a file name to be fetched from the 




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CPU Board 



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It uses only standard parts. A sample BIOS for CP/M 68K is available on disk for $20. The board works 
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20 



The Computer Journal / Issue /^22 



current disk drive, and executed. If an internal command 
verb is matched then we must jump to the verb's 
subroutine for execution. 



INC HL 



H, (f4.) 
U.A 



IfCMnd it: g«t loM-ordw part 

t9«t hiqh-ard«r part 

I star* hiqh 

I star * lOM 

(•"•cut* ccp routin* 



We then load the low order byte of the address into the 'A' 
register, from memory, increment 'HL' which then poin- 
ts to the high order byte of the 16 bit address, into the 'H' 
register. We then load the low order byte stored in the 'A' 
register into the 'L' register. Having loaded the address 
of the verb's subroutine into the 'HL' pair we jump to 
where HL is pointing. Because we have placed our "way 
home" on the stack we can return to the main loop of the 
CCP by executing a RET instruction. 



» •ntry point for rvstwtinq ccp and logging 



default dri 



RSTCCP: XOR 



<CeUFF),A 
DL06IN 



) 1 og in cl9* au 1 1 dn 



RSTCCP is where we return from most internal com- 
mands. When a file is used as the verb the program 
generally exits to the warm boot loop which rewrites the 
CCP and enters it where we originally entered. For those 
functions that ret\im here, the first thing we do is make 
damn sure that the command line character byte is 
zeroed out. We don't really need to do this, as we will just 
reset it again when we get backup to RESTRT, but some 
programs return to the CCP, and do not terminate to the 
BIOS warm boot function, or have mystical, magical 




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ways of trying to re-execute the restart command. In an 
over-kill mode I went in and put "dummy traps" 
everywhere to make sure that the two restart commands 
are only executed when and where they were supposed to, 
every time they were supposed to. When reliability is an 
issue, a little redimdant code can sometimes help. . . . 

Having once again managed the restart commands, we 
want to reassign the system disk drive, drive 'A' or zero, 
as the current disk drive. We then "fall into" RCCPNL, 
which may also be used as a CCP return point when a 
command does not wish to reassign the disk drive being 
used in the execution of a conmiand. You will note that 
there are sections of code that may not always seem 
needed in my CCP. This is because I modify it for nearly 
every specialty system I create. When we begin 
designing our own commands, you may see why these 
sections of code are left here. 



1 antry 


point 


far rwatart 


ng 


cc 


p Mithout logging in da^ault 


dn va 




RCCPT«_: 


CALL 

LD 

SUB 

LD 

OR 

JP 

JP 


eCMCR 

A, <FCBFN) 

^«.,TEMPDR 
(HL) 

N2, ERROR 
RESTRT 






laxtract navt tokan from cot 


■«and I 






Igat ♦irat char o* tokmn 
lany char'' 







Well, this pretty well covers the main loop of the CCP. 
In Part Two we will discuss the various support routines 
called by the main loop. If we have the space we will also 
begin discussion of how to design your own CCP com- 
mands to suit your specific application. 

I would recommend that you acquire the CCP source 
code, and do some snooping before we meet again. By the 
time we finish with the CCP section of our series you will 
have a great understanding of this module, and be able to 
modify it to suit yourself, with far more computing power 
than any standard system could have. Remember that, 
unlike the CCP's big brother ZCPR3, our system does not 
require any additional memory space, nor direct support 
files on your disk. When thinking of all the fun we can 
have reworking the CCP, just think of what can be done 
when we begin discussions upon the design of the BIOS 
and DOS systems! ■ 



* •• 



NEW-DOS Disks AvaUable 

An AMPRO format 5V4 DSDD with the files for the 
Crowe assembler and the CCP is available from The 
Computer Journal for $10 postpaid. Inquire about other 
formats. 

Additional disks with the BDOS and BIOS portions of 
NEW-DOS will be made available when these portions 
are published. Anyone making extentions to NEW-DOS or 
implementing it for other systems are urged to send their 
material to TCJ so that it can be shared with others. 

Tom is preparing a user disk library for the AMPRO 
little board, and the disks will be distributed by TCJ. 
Watch for more details in the next issue ! 



The Computer Journal / Issue m 



21 



Variability In The BDS C Standard Library 

Porting BDS C To CP/M 86 

By Donald Howes 



1 his overview is aimed at C programmers who don't 
own a copy of the BDS C compiler, but stiU wish to be able 
to compile some of the large number of programs which 
are available from the group, and not become old before 
their time in doing so. If you are like me (I do most of my 
work in CP/M-86, using the SuperSoft C compiler), the 
following scenario has occured at least once (and 
possibly, many times). On getting your latest software 
disk from the group, you immediately try to compile a 
program. Everything works through the compiler, but 
then comes the link step (maybe an assemble step first, 
but why make things overly complicated). You think the 
machine is having a fit, but it's fascinating, who could 
have thought that a three hundred line program could 
have generated four pages of link error messages 1 ! 

Ok, maybe that is a little overblown, but it really can be 
a problem getting a BDS C program to link and there are 
some programs which I had given up on trying to get to 
work (if you want to know, Roff is one, I really wasn't 
lying about the four pages of linker errors) . I've managed 
to solve the problem in a remarkably easy way. I've 
bought a copy of the BDS C compiler. This, however, may 
not be a viable alternative for people who are either short 
on cash, or don't have a machine which will run both 
eight and sixteen bit software (I use a CompuPro 
(Viasyn, who's Viasyn?) 8/16-A). Hopefully, this over- 
view will help to alert those people who do not have ac- 
cess to a BDS C compiler to the variations in the "stan- 
dard library" . You will notice the quotes ; one thing that I 
did find out is that there really isn't such a thing as a 
standard library. What I was able to do was compare the 
BDS C library functions to the two CP/M-86 compilers for 
which I have documentation (SuperSoft and Digital 
Research) and note the variability over the three com- 
pilers. The SuperSoft documentation states that they 
have attempted to stay as close as possible to the Unix 
library, while Digital Research is missing a number of 
Unix C functions and have implemented some specialized 
functions (there are three variations on creatO, for 
example) to take the place of a single Unix function. With 
this type of mix (admittedly, not a scientific sample, but 
you (k) the best with what you've got) I was able to break 
the library functions up into three types. First, there are 
the functions which all three compilers agree on. Given 
the differences between the compilers, I felt that these 
should represent as close to a "standard" function as 
there is. These functions will be noted by their con- 
spicuous absence from the following list. Second, there 
are the functions which both BDS C and one of the other 
two compilers define in the same way (from my over- 
view, this is generally the SuperSoft compiler), while the 
other compiler either does not support the function (the 
normal case) or the definition is different. Third, the 
cases where both the CP/M-86 compilers do not support 



the function, or the definition of the function is different. 
These are the ones which will cause the most trouble and 
I will flag the entry with two asterisks preceding the fun- 
ction name (i.e. **peek(n) ). 

Finally, a short note about syntax. The initial section 
headuig where the function name is given will name the 
function with its list of parameters as they are given in 
the BDS C User's Guide (i.e. sleep(n) ). If I refer to any 
fimction by name in the descriptive material foUowing 
the section heading, no parameters will be given (i.e. 
sleep( ) ) . Please don't assume from this that there are no 
parameters for that fimction. Also, any parameters that 
are mentioned in text will be surrounded by single quotes 
(i.e. for sleep(n) the parameter 'n' would be quoted). In 
deference to those who will be rummaging thnxigh this 
listing in the small hours of the morning, I have taken the 
liberty of rearranging the functions from their 
categorical order as found in the User's Guide into 
aljdiabetical order. 

A Note on Buffered I/O Functions 

In the foUowing list, only those functions which do not 
have the same number of parameters being passed are 
shown. However, there is a general difference between 
the way BDS C handles buffered I/O and the "standard" 
form of those functions. As is mentioned below, the BDS 
C version of fopenO does not pass a mode parameter 
when opening a file. The "standard" version of this fun- 
ction has the form: "fopen(filename,mode,iobuf)" and 
returns a valid file descriptor, which is vaed by all other 
buffered I/O functions to reference the opened file. BDS C 
buffered I/O functions do not use a file descriptor, but 
rather, directly reference the I/O buffer 'iobuf (fopenO 
does return a file descriptor, but it is not used for other 
than error checking, since 'iobuf itself maintains a copy 
of the file descriptor for use by other buffered I/O fun- 
ctions) . It may be necessary, therefore, for you to place a 
'mode' parameter in your buffered I/O calls, for them to 
operate correctly, check your compiler docimientation. 

aUoc(n) 

Returns a pointer to a block of memory 'n' bytes long. 
This is the dynamic memory (heap) allocation function 
used by BDS C. However, this function is obsolete and 
being dropped from the standard libraries of some com- 
pilers. You should use caUocO at mallocO instead of 
alloc( ) , if they are available in your compiler. 

**caU(addr,a,h,b,d) , calla(addr,a,h,b,d) 

Both of these functions are used to call a machine 
subroutine at location 'addr' . If used outside of the CP/M- 
80 environment, almost anything can happen, none of it 
good. The best that can be done is to try to determine 
what the routine was to do, and recode in standard C. The 



22 



The Computer Journal / Issue #22 



use of these functions makes the program essentially un- 
transportable ( at least, not easily) . 

••cfsize(fd) 

The function calculates the exact number of sectors in 
the open File given by the descriptor 'fd', without affec- 
ting the associated R/W pointer. 

••codend( ) .extemsO ,topofmem() ,endext( ) 

I have grouped these four functions together, since they 
all deal with the calculation of different areas of memory 
fpr dynamic use in a program. These functions could 
cause real problems, but they're so handy that they will 
almost invariably be used if the situation is appropriate. 

Codend( ) and extemsO are essentially equivalent fun- 
ctions. Codend returns the first byte following the 
program code and extemsO returns ttie first byte of the 
external data area. These wiU normally be the same, 
unless the external data area has been explicitly moved 
( this could be done so the code could be ROMmed) . 

TopofmemO returns a pointer to the last byte of user 
available memory (generally the base of the BDOS in 
CP/M-80), while endextO returns a pointer to the byte 
following the external data area. You can see that the use 
of these two functions will allow for the calculation of the 
amount of space in the system which can be used as heap 
space. 

Some compilers may not have any of these functions 
available, or some may be present but the action of the 
function may be different (for example, the SuperSoft 
compiler has a function named topofmemO, but it fun- 
ctions the same as endext( ) in BDS C) . If your compiler 
has a way of determining the top of the external data 
area, and you are using a small memory model (for 16-bit 
compilers) , the size of the heap area can be found by sub- 
tracting the top of the external data area from OxFFFF 
(the top of the data segment in a small memory model). 
My thanks to John Johnson of Professional Microware, 
who pointed out this fix. 

**creat( filename) 

Creates the file of name 'filename', erasing any 
existing file which already has that name. Your compiler 
may require an additional parameter after 'filename', 
the mode in which the file has been opened. Check your 
compiler documentation for the parameter list. 

••csw( ) 
Returns the byte value of the console switch register. 

•*ermo( ), errmsg(ermum) 

Does the same as the external variable ERRNO and the 
function perror(s) combination found in other compilers. 

•*exec v ( f ilename,argvector ) 

This function allows the passing of a variable number 
of argiiments to the chained program 'filename', by 
passing 'argvector' a pointer to an array of string poin- 
ters. This could require a real software kludge to port a 
program. 

••exitO 
If there is one function that I would have thought would 



have been standard between compilers, it is exitO. No 
such luck, each of the three compilers handled the closing 
of files and flushing of buffers in a different way. In BDS 
C, exitO wiU close all open files, but does not flush any 
buffers. This means the a BDS C program will have a call 
to fflushO to empty any buffers before a call is made to 
exitO. This may not be necessary for you. Check your 
compiler documentation to see just how exit( ) functions 
in your compiler. 

••fabort(fd) 

The fimction frees the file descriptor 'fd' without 
closing the file. This function was present in the Super- 
Soft compiler, but only to maintain some compatability 
with BDS C. It's not a great idea to use this function even 
if it's present in your library, since some or all of the file 
input can be lost if the file had been opened for writing. 

•*fcreat(filename,iobuf) 

Creates the file 'filename' and opens the file for buf- 
fered output using a buffer pointed to by 'iobuf . The size 
of the buffer is determined from the BDSCIO.H variable 
BUFSIZ. This function is needed, since the BDS C version 
of fopen( ) does not support the mode parameter. A call to 
fopen of the form "fopen(filename,mode,iobuf)", where 
mode is declared as "w" (write only) would accomplish 
the same. See below for the BDS C version of fopen( ) . 

••fgets(str,iobuf) 

Reads a line from the input buffer 'iobuf' and loads it 
into the string pointed to by 'str'. A third parameter 'n' 
( the number of bytes to be read) may be required by your 
compiler. The BDS C version reads the buffer until an end 
of line is found in the input stream, not until a specified 
number of bytes have been read. The alternate version of 
fgetsO has the form "fgets(str,n,iobuf)". 

••fopen(filename,iobuf) 

Opens the file 'filename' for buffered input and 
initializes 'iobuf', the input buffer. This function does not 
implement the file I/O mode parameter and, therefore, 
may be a parameter short for your version of fopen( ) . 
The alternate version of fopen has the form 
"fopen( filename,mode,iobuf ) " . 

getcharC ) 

The BDS C version of getchar( ) tests for " C and re- 
boots the operating system if found. My other compilers 
don't, so if you wish to do this type of interrupt test, it 
would have to be coded explicitly. 

••getline( strbuf .maxlen ) 

Returns a text line of characters of maximum length 
'maxlen' into the space pointed to by 'strbuf'. This seems 
to be a special case of gets (), with the maximum line 
length given as a parameter (there is an automatic 
return with getlineO when 'maxlen' is reached). GetsO 
could be used in place of getline( ) , though you would have 
to watch that the length of the string did not exceed the 
size of the array into which it was being read, since gets( ) 
does not check this. 



The Computer Journal / Issue #22 



23 



getval(strptr) 

'Strptr' is a pointer to a pointer of a string of ASCII 
characters separated by comma's. This is the driving 
routine used by initwO and initbO to fill their arrays. 
This function probably won't be present in compilers 
which allow initiahzation (see the descriptions of initbO 
and initwO, below). 

initb(array,string),initw(array,string) 

These functions are used to perform the initialization of 
character and integer arrays respectively. They are not 
needed in compilers which allow the initialization of 
arrays at the time they are declared. 

inp(n),outp(n) 

The functions read and write 8-bit values to the port 'n'. 
If these functions are not present in your compiler, it 
would be possible to accomplish the same thing by the use 
of pointers. 

isspace(c) 

Tests whether the character 'c' is space, tab ( \ t) or 
newline ( \ n) character. This same functions may be 
called iswhite( ) in other compilers. 

khbitO 

Polls stdin to see if there is a character present, returns 
TRUE orFALSE. 

movmem(source,dest,count) 

Moves 'count' bytes of memory from location 'source' 
to destination 'dest'. The original memory is not 
modified, unless the destination area partially overlies 
the source. 

••oflow(fd) 

Quoting the manual "returns true (non-zero) if an over- 
flow has occured into the high order (third) byte of the 
random-record field of the FOB" . Good luck. 

**open(filename,mode) 

Opens the file specified by 'filename' for I/O as given 
by 'mode'. However, the meanings of the mode values are 
different in BDS C. BDS modes are: = input (write 
only), 1 = output (read only), 3 = input/output 
(read/ write). 

pauseO 
Tests for console input, looping until a key is pressed. 

**peek(n), poke(n,b) 

These are equivalent to BASIC PEEK and POKE stet- 
ments, and are not really necessary, since C supports in- 
direction. Peek(n) can be simulated by initializing a char 
pointer: 

char *bdosjmp = 0x05; ' 
This won't work in BDS C or other compilers which don't 
support initialization. If the compiler doesn't support 
initialization use: 

char'bdosjmp; 

bdosjmp = (char •) 0x05; 
(This will only work in the 8086 environment if the DS 
register points to the correct segment. This can't be 



guaranteed). 

As is pointed out in the BDS C manual, poke( ) is better 
accomplished by using pointers : 
♦n = b; 

putchar(c),putch(c) 

The BDS C version of putchar( ) is able to detect the in- 
put of " C (and ^ S) during character output. Putch( ) does 
not detect these control characters. A call to putcho, 
therefore, is equivalent to putcharO in other compilers. 
If you want to be able to interrupt character output, you 
will have to code an explicit test into the output loop. 

qsort(base,nel,width,compar) 

This function is used by BDS C to conduct a shell sort. 
The type of sort that is conducted may be different for 
your compiler (Digital Research does a quick sort) even 
though the function name is the same. Check your com- 
piler documentation. 

*»read(fd,buf,nbl) 

Reads the number of blocks given by 'nW (1 block = 
128 bytes) from the file given by the file descriptor 'fd' in- 
to the buffer 'buf'. Other versions of readO require the 
number of bytes to be read as the final parameter, rather 
than the number of blocks. To pass a valid parameter, 
multiply the value of 'nbl' by 128. 

rename(old,new) 

Renames the file given by filename 'old' to that given 
by filename 'new'. Although there are obvious advan- 
tages to this function, it is not supported by Digital 
Research, and possibly not by your compiler. Check your 
compiler documentation. This could be accomplished by 
a BDOS call to change the FCB. 

**rsvstle(n) 

The function limits the closest approach of the stack 
(which grows down from the top of memory) and th 
heap (which grows up from the end of the external dat 
area) to 'n' bytes. Stack/heap management of this type 
generally the responsibility of the programmer. 

••setfcb( fcbaddr,filename) ,fcbaddr( fd) 

Setfcb( ) initializes a CP/M FCB with the string pointe 
to by 'filename', while fcbaddrO returns the address c 
the FCB pointed to by 'fd' . 

setmem ( addr,count, byte ) 

The function sets 'count' contiguous bytes starting at 
'addr' to the value of 'byte'. This function is used to 
initialize buffers and arrays. It is not needed in compilers 
which support initialization. 

sleep(n) 

Suspends the execution of a program for a variable 
amount of time. Since how the time delay is calculated is 
compiler and processor dependent you should consult 
your compiler documentation. 

**ungetch(c) 

The character 'c' is placed on the console buffer and is 
returned by the next call of getchar( ) . This function may 



24 



The Computer Journal / Issue #22 



be called ugetchar ( ) or ungetchar( ) by your compiler. 

••write(fd,buf,nbl) 

The function writes 'nbl' blocks from the memory 
location pointed to by 'buf to the file pointed to by 'fd'. 
Other versions of write pass the number of bytes to be 
written, rather than the number of blocks. It would be 
necessary to multiply the value of 'nbl' by 128, to obtain a 
valid parameter. ■ 



The C Users' Group 

The above article was reprinted from The C Users' 
Group (CUG)September, 1985 newsletter, with their 
permission. A language is only as good as what you can 
do with it, and CUG maintains a large library of very 
useful programs. We will be reviewing and commenting 
on some of their disks in the future, but you should con- 
tact Donna Stucky Ward at The C Users' Group, Box 97, 
McPherson, KS 67460 for details on joining the group and 
a catalog of their disks. 

Starting with the next issue Donald Howes will be 
writing a column on C language programming, and we 
would appreciate your comments and suggestions on the 
topics to be covered. We would also like to include your 
tips, routines, and questions. 



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The Computer Journal / Issue #22 



25 



The SCSI Interface 

Introductory Column To A Series 

By Rick Lehrbaum 



X research the history of SCSI, I 
had lunch with Larry Boucher, the 
founder of SCSI. It all began in the 
Spring of 1979 when Larry was the 
Director of Design Services at 
Shugart Associates, and Shugart 
was getting ready to announce 
another new Winchester disk drive 
product. As usual, it would take IV2 
to 2 years before Shugart could enjoy 
widespread sales of the new drive 
since it took that long for all the con- 
troller designers to debug their 
phase-locked loops. But that was the 
way it had to be back then— there 
was no standardized I/O bus in the 
micro world. (Unless you want to 
count RS-232!) 

Larry decided that what Shugart 
needed was a way to speed up con- 
troller design. Before coming to 
Shugart, Larry had worked at IBM, 
and it occurred to him that 
something like the IBM OEM Chan- 
nel also made sense for micro's. So 
Larry, along with Bemie Nieman 
(who worked for Larry) and Jim 
Korpi (who worked for Bemie), 
wrote the spec for a new interface to 
be proposed for all future Shugart 
disk controllers. They called it the 
Shugart Associates Standard Inter- 
face, or "SASI." According to Larry, 
there were two major objectives in 
defining SASI: (1) Make it the 
cheapest possible interface with an 
8080-Iike bus; and (2) Outperform 
the IBM OEM Channel bus, which 
ran around 500,000 bytes per second 
average throughput. Both goals 
were met. 

The rest is history. Shugart of- 
ficiaUy adopted the new SASI inter- 
face in July 1979, and commissioned 
Data Technology Corporation (DTC) 
to do the first SASI disk controller in 
August 1979. DTC performed ad- 
mirably, under the direction of Dave 
Tsang, delivering samples of the 
new SASI controller board to 
Shugart in December, followed by 
delivery of 25 production boards in 
January 1980. A new industry stan- 
dard was bom. But few knew it. . . 



In July 1981, NCR began taking an 
interest in SASI. In December 1981, 
John Lohmeyer (NCR) and Hank 
Meyer (Shugart) formally proposed 
to the American National Standards 
Institute (ANSI) that it adopt SASI 
as a small computer intelligent 
peripheral interface. An ANSI 
committee called "ANSC X3T9.3" 
was in the process of defining "The 
next microcomputer I/O interface." 
They tumed SASI down! It seemed 
all was lost. 

But there was another ANSI com- 
mittee, currently inactive, which 
had been chartered to define a 
microcomputer "peer-to-peer" 

protocol. "ANSC X3T9.2," as this 
other committee was called, took 
SASI under its wing, in February 
1982. One of the first official orders of 
business was to change SASI's 
name, since it contained Shugart's 
name. They settled on "Small Com- 
puter System Interface." 

In the months that followed, ANSC 
X3T9.2, under the able direction of 
Bill Burr (National Bureau of Stan- 
dards), hammered out a thorough 
and percise specification (currently 
over 180 pages long!) which makes 
SCSI one of the bext docimiented in- 
terface standards in the computer 
industry. 

Last summer, the members of 
ANSC X3T9.2 unanimously approved 
the standard, forwarding it to the 
ANSI parent organization for public 
review and final approval. Short of 
editorial and other minor correc- 
tions, the final SCSI specification is 
in hand. 

And now, a few questions from 
readers... 

WhattoSCIS? 

SCSI stands for "Small Computer 
System Interface" and is quickly 
becoming the most popular interface 
for connecting hard disk drives to 
small computers of every type. But 
as you'll see later, SCSI can be used 
for a lot more than that. 



Why should I use SCSI? 

You should use SCSI if you need an 
easy way to make your computer or 
computerized device expandable. 
Today, SCSI is mostly used for ad- 
ding hard disk and tape controllers 
and drives. But soon, there will be 
lots of other functions to choose 
from, including: optical storage, 
network interfaces, graphics 
displays, co-processors, and more. 

SCSI has a number of important 
advantages over other ways of at- 
taching add-on's to a small computer 
system. One of the biggest advan- 
tages of SCSI is that is is an easy and 
inexpensive interface to add to any 
computer. It also simplifies your sof- 
tware hassles: when implemented 
correctly, SCSI allows you to change 
from one brand of device (such as a 
hard disk controller and drive) to 
another, with little or no software 
modifications. 

How do you pronounce "SCSI"? 

I'm glad you asked that question! 
There has really been a lot of time 
and energy arguing about how to 
pronounce SCSI. Well, it pretty 
much boils down to either pronoun- 
cing the word SCSI as SKU-zzy, or 
spelling it out S-C-S-I. My own per 
sonal preference is "SCSI." On the 
other hand, surveys show that 78% of 
corporate marketing executives 
prefer spelling it out. 

Where can I get more information? 

You have two choices: (1) Read 
this colunm in The Computer Jour- 
nal, or (2) Be the fvst one on your 
block to have an official copy of the 
"ANSC X3T9.2 SCSI Specification," 
by sending $20, along with a self- 
addressed mailing label to: X3 
Secretariat, Computer and Business 
Equipment Manufacturers Assn., 
311 First Street NW, Suite 500, 
Washington, DC 2000L 

Watch for "An Introduction to SC- 
SI" in the next issue of The Com- 
puter Journal, and send your 



26 



The Computer Journal / Issue #22 




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Editor at TCJ or to Rick at the 
following address. ■ 

Rick Lehrbaum 

VP of Engineering 

AMPRO Computers, Inc. 

PO Box 390427 
Mountain View, CA 94039 

SCSI NEWS 

This section will bring you the 
latest news and information about 
SCSI related products and ap- 
plications. Your input and experien- 
ces will be greatly appreciated. 

SCSI RAM-DISK— The AMPRO SC- 
SI/RAM suitable for use in both 
single- and multi-master system ap- 
plications is available with either 
512K bytes or 1 megabyte of RAM, 
and can be used in any system 
having an SCSI (SASI) interface. By 
adding one or more SCSI/RAM units 
to a host computer, system memory 
need not be used as a RAM disk, 
thereby freeing the computer's 
system RAM for program functions. 
Data can be transfered over the SCSI 
bus at up to 1.5 megabytes per 
second, and effective SCSI/RAM 
disk transfer rates are generally as 
fast as when using system RAM. In 
addition, the SCSI/RAM does not 
clear its memory on SCSI bus reset, 
thereby allowing the SCSI/RAM to 
be used for system memory backup 
on power-fail detection. 

Inexpensive SCSI host adapters 
aUow connection to a wide variety of 
host computers, including the IBM- 
PC and AT, VME-bus, Multibus, and 
S-100. The SCSI/RAM, with 512K 
bytes of on-board RAM occupies a 
single 5V4 X 7% inch circuit card, 
and has the same mounting holes 
and footprint as industry standard 
5V4 inch disk drives. A daughter 
board may be added to expand the 
RAM disk size to 1 megabyte. 
Available for $395 from AMPRO 
Computers, 67 E. Evelyn Ave, Moun- 
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SCSI Printer Server— The AMPRO 
SCSI/PRN intelligent printer server 
is suitable for both single- and mulit- 
master systems. Up to seven SCSI 
hosts can connect to a single SC- 
SI/PRN, sharing printer and spool 



buffer resources, and maximum 
data transfer rate is 1.5 megabytes 
per second. The SCSI/PRN's three 
printer interfaces allow 

simultaneous connection of one Cen- 
tronics compatible printer and two 
RS232C serial printers, with host 
controlled baud rates of up to 19.2K 
baud. Onboard memory of 512K 
bytes, expandable to 1MB via 
daughter board, is used as a spool 
buffer. Available from AMPRO for 
$449. 

SCSI Real-Time I/O-The AMPRO 
SCSI/IOP is an intelligent processor 
which adds read-time control and 
measurement capabilities to any 
computer system having an SCSI in- 
terface. The SCSI/IOP plugs into a 
normal STD bus card cage, and can 
control STD bus I/O boards such as 
analog-to-digital converters, video 
display controllers, speech syn- 
thesizers, network interfaces, etc. 
Low cost SCSI host adapters are 
available for many computer 
systems, and SCSI's bus arbitration 
feattu^ permits up to eight host 
computers and SCSI/IOP's to share 
resources. 

The SCSI/IOP includes a 4 or 6 
mHz Z80 microprocessor, eight byte- 
wide memory sockets for up to 64K 
of EPROM/RAM memory, and a Z80 
counter/timer controller. Fimrware 
on the SCSI/IOP supports a number 
of basic operations, and both the 
Initiator and Target functions of SC- 
SI which include peer-to-peer 
message capability. The SCSI/IOP 
can be used in hierarchical real-time 
control system configurations, or 
where either host or I/O device 
redundancy is required. Available 
from AMPRO with preliminary 
pricing of $119. 

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with fan & supply, and cables is 
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for $599 from Peripheral Land, 3400 
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95051 (408) 248-5282. ■ 



The Computer Journal / Issue #22 



27 



Indexed Sequential Access Method Files 

Using Turbo Pascal ISAM Files 

By Jerry Houston 



ISAM, or Indexed Sequential Access Method, files are 
the type most commonly used for business purposes on 
large computers. ISAM file records are accessed accor- 
ding to a KEY FIELD for reading, writing, or updating. 
This method provides random access to the file records, 
aUowing simple updates and quick retrieval of a par- 
ticular record. 

Operating systems that support ISAM files directly are 
usually found on minicomputers and mainframes. There 
is certainly a cost to pay in terms of overhead (both in 
processing requirements and in media space), but the 
advantages are generally thought to be worth the cost. 

In the simple example that accompanies this article, 
an ISAM-type file is set up as a phone directory. The key 
field in each record is the name of a person or a company, 
and the rest of the record contains just a phone number. 
Now, if the prospect of another phone list program 
doesn't exactly make your floppies quiver, consider that 
you can easily define more fields for the file, and the key 
field can be anything you want it to be— a name, em- 
ployee number, stock number, or nearly any other infor- 
mation upon which you'd like the file to be organized. 

Taking that modification a step further, the index for 
the file could be checked to see whether it INCLUDES a 
particular key word— easy to do in Turbo Pascal— and a 
large file of The Computer Journal articles could be sear- 
ched for a particular content. 

In the large computer systems that support ISAM files 
directly, the key fields are checked against two or more 
kinds of index on the disk drive itself. The desired KEY 
FIELD is compared to the entries in a short sequential 
file called a CYLINDER INDEX, which lists the upper 
limits for the key fields that are located on a particular 
C¥LINDER (the same track extended through all the 
recording surfaces of the disk-pack). Once the head ac- 
cess mechanisms have positioned the read-write heads to 
access a particular cylinder, then a track index is con- 
sulted to determine the track on which the desired record 
can be found, and the proper read-write head is elec- 
tronically switched into action. Then it's just a matter of 
waiting until the right record rotates under the head, a 
delay called latency, or rotational delay. 

A big advantage of ISAM files over ordinary sequential 
files becomes apparent when it's necessary to update 
one. A sequential file must be re-created in its entirety 
just to change a single record. Records in an ISAM file 
can be re-written, making it easy to correct fields in in- 
dividual records. It's almost too obvious to point out, but 
applications that require access to a limited number of 
records from a large file are better served with random- 
access files (such as ISAM), so that aU the previous 
records don't have to be examined in order to find the one 
that's needed. 



Random Access On Micros 

Most smaU computers have random access capability, 
but somehow the program needs to determine which 
record is to be read (or written). Random files can be 
DIRECT ACCESS FILES, in which case the program 
identifies the exact physical location (track and sector) 
where the record is located, or they can be RELATIVE 
FILES, where each record number is relative to the 
beginning of the file. The computer already must know 
how long each record is, and it can find the 29th record in 
a relative file by passing over the first 28, then accessing 
the next. 

The trouble with this is, how is the computer to know 
that the address and phone number for XYZ, Inc. is in 
record number 127, or that the record for product number 
C-12285-BR is located on track 2A, sector 09? The answer, 
of course, is that it needs an INDEX, as in ISAM. 

Using the relative files that are available with every 
disk-equiiq)ed computer, and accessible from every 
language, it's possible to duplicate the ISAM function 
with applications programming. This requires keeping a 
small sequential file on the disk that ctHitains the key 
fields and corresponding record numbers of the main 
(relative) file. At the beginning of the program, and 
whenever the file is updated, the index file is read into a 
table in memory which can be searched to find the 
location of whatever record is needed. If a file is designed 
for direct-access, then the index must contain the key 
field and the physical track location where the record can 
be found. Since relative files are easier to work with and 
more versatile in some respects, this article will concert 
itself with simulating ISAM with Turbo Pascal relative 
files. 

Program ISAM.PAS 

The Turbo Pascal program that accompanies this ar- 
ticle maintains an ISAM file of names and phone num- 
bers in such a way that the user can type in a name (the 
KEY FIELD) and the computer will deliver up the phone 
number associated with it in the file. 

This example program was purposely kept simple, but 
it would be an easy matter to expand the records in the 
ISAM file to hold whatever information is required for a 
more complex application. Once we've covered the 
example program in detail, I'll mention a way to make it 
even better, if you're so inclined. 

Portability of Code 

In keeping with my philosophy that a programming 
process (design, coding, testing) shouldn't be done twice 
if once will do, I've written the procedures and functions 
of the accompanying program with local variables and 
parameter lists (also called argument lists). Thus, these 
sections can be stored separately in a Pascal library and 



28 



The Computer Journal / Issue #22 



used whenever a progranuning project requires ISAM 
files. They can be read into the source code being 
developed, and made a part of the new program with 
relatively little effort. If GLOBAL variables (rather than 
passed parameters) are used, each procedure and fun- 
ction will need to be modified extensively to agree with 
the variables used in every new program. 

Run-Time Narrative 

When ISAM.PAS is compiled and run, it will look for an 
index file that shares the name of the ISAM file being 
used. The ISAM file will have an extension of .ISA, and 
the matching index file will end with .KEY. The first time 
the program is nm, of course, neither of these files will 
exist, and the file-read sections are coded to understand 
this. 

The menu that appears at the beginning of the program 
will offer the choices : 

Q=Quit R=Read A=Add 
D=Delete C=Change 

ADD will write new records to the ISAM file. The user 
is prompted for a name to be used as the key field, then 
the phone number to be stored with it. The name and 
PHONE number go into the PHONE.ISM file, the name 
and the RECORD number (from the ISAM file) go into 
the PHONE. KEY file, and also into the table of keys 
that's maintained in memory. Trying to add a new record 
that has the same key field as an existing record is a big 
no-no for ISAM file processing, so an appropriate error 
message is displayed if this is attempted, and the ad- 
dition is not made. 

DELETE will not remove a record physically from the 
ISAM file, nor its key from the index, but it will replace 
the phone number with a message that says it's been 
deleted. This function of the program could be changed so 
that the record actually IS deleted (at least, used for the 
next ADD), but at a cost of additional complexity that 
isn't warranted in such an example. Trying to delete a 
record that doesn't exist is taboo, and earns the user a 
scolding from the computer. 

CHANGE allows the phone number to be edited. In a 
more complex application you would want to allow 
editing of all the fields EXCEPT the KEY FIELD. If that 
needed to be changed, a DELETE would be appropriate 
instead. Naturally, an attempt to change a record that 
doesn't exist is useless, and will be trapped as an error 
condition. 

QUIT is just a graceful way out of the program, back to 
the operating system. From the menu part of the 
program there are no files to close or other End Of Job 
processing to do, so it just means a quick trip to the end of 
the main logic. All the other functions re-run the main 
logic, so that a variety of tasks can be carried out while 
the program is running. 

The Main Flow of Logic 

I wrote this program knowing that I would be ex- 
plaining it in detail in this text, so it isn't as full of com- 
ments as it ordinarily would be. Remember that you'll 
probably want to use this code again and again, so it 
wouldn't hurt to add additional comments as you enter 



the source. A few extra minutes of typing now can save 
hours of debugging later, when you want to use this 
method to access complex files in a new application— and 
that goes for all source code. (End of Lecture, I promise. ) 

Let's take a look at the mainline logic first, that last 
chunk of code that begins with BEGIN and ends with 
END. Because this program is written modularly, the 
main logic is short and simple. (It's not easy to write 
si>aghetti-c6de in Pascal but believe it or not, I've seen it 
done!) 

LoadKeys is a procedure that reads the .KEY file from 
the disk and loads the values found there into the two 
arrays IndexAray[1..200] and KeyAray[1..200] that make 
up the file index table in memory. The array limits of 200 
were chosen entirely arbitrarily, and might be much 
higher in an application program, depending on need and 
the availability of variable storage space. You can see 
one purpose for the RetumCode that many of these 
procedures send back to their calling module— if the ap- 
propriate .KEY file can't be found on the disk, the 
LoadKeys procedure sends back a return code of — , and 
the main logic understands to print an error message to 
that effect and bail out to STOP : . 

START: is a label that tells the program where to go 
when a restart is required. This is done after all the menu 
functions except QUIT, which sends control instead to 
STOP: at the bottom. 

The line that writes the heading and menu items to the 
screen starts out with a #26 as the first item printed. 
That's a screen-clear character for many computers, and 
could have been written just as well with a control Z. 
Turbo Pascal also offers a screen clear procedure, but 
this is shorter to type. Other WriteO statements in this 
program use control M and control J to produce a 
carriage-return and a line-feed, respectively. Alter- 
nately, those could be coded as #13 and #10. 

After Choice is read, it's changed to upper case with the 
UPCASEO function that's built-in. This makes it easier 
to write the subsequent CASE STRUCTURE so that up- 
per and lower case selections will both be honored. The 
arguments of the case structure, of course, match the of- 
ferings from the menu line at the top of the screen, and all 
except 'Q' will execute a particular procedure written as 
a demo. 

That's all there is to the main logic. Thanks to struc- 
tured modular programming, a problem that's too com- 
plex to grasp aU at one time can be broken down into 
separate tasks that are easily comprehensible. Now those 
smaller tasks will be broken down further into individual 
steps with an explanation for each. 

Of Types, Variables, Functions, and Procedures 

Those who are new to Turbo Pascal (and I hope that 
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about the use of the TYPE declaration. It's pretty easy to 
understand why Turbo (or even BASIC) wants to know 
whether a variable is to be treated as a real number or an 
integer, as the two are stored differently in memory and 
in files. They require different numbers of bytes and are 
treated differently by the compiler. Fact is, a Pascal 
programmer isn't limited to the pre-declared types of 
variables that most languages provide, but is free to 




29 




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30 



The Computer Journal / Issue #22 



define types that are consistent with the present needs. 

In this program, the procedures that access the files 
will need to be passed a parameter that tells them what 
file name to look for. Since the parameter can be called 
by one variable name on the sending end, and by 
something entirely different on the receiving end, the 
procedure must be able to identify it according to (1) its 
location in the parameter list and (2) its type. Because 
I've defined a TYPE called AnyFile, a string that's able 
to contain ten characters, I can pass a file name along 
from a "calling" procedure to a "called" procedure in a 
list of arguments. The argument list specifies to the 
called procedure that the file name is first in the list, and 
also what type of variable it is. This helps to make the 
code "portable", in that it can be used in various 
programs with little or no customizing needed. 

Similarly, I'll be using a lot of string variables that con- 
tain a 30-character name and a lot of string variables that 
contain a 20-character phone number. These are defined 
as type NAME and type PHONE. 

Even entire records can be defined as a TYPE, as 
shown by the next two entries. The records in the ISAM 
file will all contain a NAME and a PHONE (which were 
previously defined as types of their own, so these don't 
need to be spelled out as to how many characters, etc.) 
and the INDEX file will contain records that each contain 
a NAME and a record number, which is of the ordinary 
type INTEGER. 

To digress for just a minute, if the number of records 
were to be limited to less than 256 for an application like 
this, it would be appropriate to use type BYTE instead of 
INTEGER for all the variables that have to do with 
record numbers and counters. Each variable would then 
require only one byte of storage or memory instead of 
two. 

Now comes the familiar declaration for all the 
GLOBAL variables in the program, the ones that are to 
maintain their values from one procedure to the next. As 
you can see, there are some variables that are declared 
as ordinary types, such as INTEGER, and others that are 
declared as the special types that were defined above. 

FINDEXO 

FINDEX is my shorthand for Find Index, a function 
that searches through the table of key fields, and for each 
key requested finds the appropriate record number in the 
ISAM data file. It's a function, rather than a procedure, 
because of the way it's written and used. When the ap- 
propriate parameters are passed to this function, 
referring to FINDEX( ) is all that's needed to get an an- 
swer. One way of thinking of it is that you RUN a 
procedure, but you MAKE USE OF a function. To find the 
record number for a variable called NameIn, for exam- 
ple, from among MaxKeys number of entries, all we need 
to say is: 

RecordNumber : = FINDEX(NameIn,MaxKeys) ; 

and we can use a function anywhere a variable would be 
at home, such as: 

Write(FINDEX(NameIn,MaxKeys) ) ; 



FINDEX begins by initializing COUNT to 0. Since 
COUNT is declared as a variable within the function 
FINDEX, it is LOCAL to this function. Even though there 
are other variables called COUNT elsewhere in the 
program, they won't get confused. This is one of the 
reasons why functions and procedures that use local 
variables are so portable from one program to another. 
FINDEXCode and FOUND, a Boolean truth flag, are also 
declared here, and exist only within FINDEX. 

From there on, it's a relatively simple function, and 
even TurBeginners (sorry, I just couldn't resist, and this 
IS supposed to be a tutorial...) won't have any problems 
with the logic. The only line that's not entirely clear is the 
one that actually compares the given name with the 
names in the table. It starts out with : 

If Copy(KeyAray[Count] ,l,Length(IndexKey) ) 
= IndexKey then... 

Rather than requiring the given name to be an exact 
match for the key field, I've written the program to allow 
a partial— BUT CORRECT— name to be used instead. 
The comparison is made to the key fields in the table only 
up to the length of the given name. That way, I can find 
the phone number for "Remote Measurement Systems, 
Inc." by typing just "Rem", if I'm sure that none of the 
other records starts with the same three letters. If there 
aren't any others that start with "R", I could just type 
that, but that would be taking a fair-sized chance. I need 
to enter enough of the name that there is no question 
which record is required, as the program will read the 
record that corresponds to the first match it makes. 

LOADKEYS 

LoadKeys is a procedure, so it's something to RUN, not 
USE. The program doesn't expect LoadKeys to take on a 
value like a function, although this procedure does, in 
fact, pass a RetumCode back to the calling module. The 
return code goes back under its own variable name, not 
the name LoadKeys. The object of this procedure is to 
read the .KEY file from the disk and load the values it 
finds there into the two arrays that make up the index 
table in memory. 

Following the procedure name is a good example of a 
parameter list. I'll discuss just this one in detail, and 
you'll be able to see the similarity between this one and 
the parameter lists in the other procedures. 

First of all, if the procedure is to load a file into 
memory, it needs to know from which file to read. The 
file name COULD have been declared as a global 
variable, but then it would have to be done that way in 
every program that makes use of this procedure, and the 
procedure would be workable only with one file name per 
program. Instead, the file takes on the name that this 
procedure associates with the parameter FileName, 
which is defined as type AnyFile. The calling logic can 
place a literal value, such as a file name of 'PHONE' in 
the first spot in the parameter list, and the called 
procedure will find it there. 

The other way of passing these parameters is shown 
next, with two parameters passed as variables. There are 
a lot of procedures in this program that make use of the 
variables MaxKeys and RetumCode, which have already 



The Computer Journal / Issue i^'22 



31 



been explained, and it's easiest to pass those back and 
forth as variables in the parameter list. I happen to use 
MaxKeys and RetumCode for the very same purposes 
each time I use these procedures in other programs, so 
that's not difficult. You'll notice that the keyword VAR 
precedes these variables in the parameter list, just as it 
would in an ordinary variable declaration. Of course, if I 
intend to have a program work with multiple ISAM files, 
I have to be sure that MaxKeys is assigned properly 
before this procedure is called. RetumCode gets its value 
within the procedure and passes it back to the calling 
module, so it doesn't have to be initialized before use. 

Since this procedure accesses a disk file, it makes use 
of the Turbo compiler directives {$1-} and {$1+} which 
turn off system disk error handling and turn it back on 
again, respectively. If there's a problem like "file not 
found", I want to deal with it from within this program, 
not have the operating system crash the program on that 
account. After the error-checking is turned off, an attem- 
pt to open a buffer for the file using the statement 
Reset (IndexFile) is all that's needed to see whether the 
file exists. The Turbo Pascal function lOResult will 
return a value of zero if everything was all right, or an 
I/O error number if it wasn't. If things went well, this 
procedure turns error checking back over to the system 
and continues. If they didn't, a value of -1 is placed into 
RetumCode, the parameter that will be passed back to 
the module that called LoadKeys, and control is passed to 
the label RETURN: at the bottom of this procedure. That 
calling module is written so as to understand that a 
RetumCode of -1 means the .KEY file wasn't there. 



About the only other obscure code in this procedure is 
the part that starts out with the line : 

WithlndexRecDo... 

IndexRec is defined as a variable of type INDEX, which 
means that each IndexRec actually contains the 
variables ISAMName and ISAMPhone, which are of type 
NAME and PHONE, respectively. In order to access 
these "buried" variables, we need to enclose all referen- 
ces to them between statements like the above, and an 
"End;". Otherwise, the compiler will swear that it 
doesn't know what variables we're talking about. Trust 
me, this is only confusing at first— it becomes pretty in- 
tuitive after you've used records this way a few times. 
The convenience of being able to refer to entire records 
by one variable name (such as when reading or writing to 
a fUe) is wonderful. By the way, the WITH statements 
can be nested, and if you write some lines that need to ac- 
cess variables that are shared by more than one record at 
a time (like a variable that's stored in two different files) , 
you can write it such as : 

With IndexRec, DataRec Do 



End; 

It's pretty clear, then, that this procedure reads the file of 
the same name as the ISAM file, but with an extension of 



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The Computer Journal / Issue #22 



Program ISAM; 

< Demonstration o-f reading and *»riting an ISAM-type -file with Turbo Pascal > 

Label Start, Stop; <labels used in main logic only> 



Type AnyFile = StringC103; 
Name = String[30]; 
= StringC203; 
= Record 

ISAMName : Name; 
ISAMPhone : Phone; 
End; 
= Record 

KeyField : Name; 
RecNum : Integer; 
End; 



^declaration o-f non-standard types> 



Phone 
ISAM 



INDEX 



<6LOBAL variables that retain their> 
< values throughout the program > 



Integer; 



<LOCAL variables that exist anly> 
{within the function FINDEXO > 



VAR INDEXFile : File of INDEX; 

ISAMFile : File o-f ISAM; 

INDEXRec : INDEX; 

ISAMRec : ISAM; 

IndexAray : Array t 1 .. 2003 of Integer; 

KeyAray : ArrayC1..200] of Name; 

Choice : Char; 

Name In : Name; 

F^oneln : Phone; 

MaxKeys : Integer; 

ReturnCode: Integer; 

Function FINDEX < INDEXKey: Name; Max : Integer) 

Label Return; 

VAR Count : Integer; 

FINDEXCode : Integer; 
Found : Boolean; 
Begin 

Count := 0; 
FINDEXCode := 0; 
Found := False; 
With INDEXRec Do 
Begin 

Repeat 

Count := Count * 1; 

If Copy (KeyArayCCount 3, 1, Length <IndexKey> ) = IndexKey then 
Begin 

FINDEXCode := IndexArayCCount 3; 
Found := True; 
End; 
Until ((Found = True) or (Count >= Max)); 
End; 
Return: 

If (Found = True) then FINDEX := FINDEXCode Else FINDEX :» -2; 
End; 



<' opens up' INDEXRec to get access) 
{to the variables inside it > 



Procedure LoadKeys(Fi leName: AnyFi le; Var MaxKeys: Integer ; ReturnCode: Integer) ; 

Label Return; 

W^r Count : Integer; 

Begin 

Assign<IndexFile,FileName * '.KEY'); 
{♦I-> {turns off system error — checking) 

Reset ( I ndex File); 
{«!-«-} {error -checking back on here) 

If lOResult <> then {checks whether any error happened) 

Begin 

ReturnCode := -1; 
Boto Return; 
End; 



The Computer Journal / Issue #22 



33 



.KEY, and puts the names it finds there into an array 
called KeyAray[1..200] and the record numbers into 
another array called IndexAray[l.200]. These two arrays 
make up the table in memory that is searched to find the 
appropriate record number for any name that's 
requested. 

From this point on, I'll offer less explanation for each 
procedure, just pointing out the logic that may not be ob- 
vious, and the syntax that might be unclear to someone 
starting out with Turbo. 

READISAMO 

ReadlSAM is the procedure to read the ISAM file, and 
the arguments (parameters) passed to it include the file 
name and the key field being sought, with the third 
argument— the RetumCode— that goes back to the 
calling module to identify an error. 

First the function FINDEX( ) is called, and FINDEX( ) 
will contain either the value of the record number for the 
key field that's wanted or a return code that indicates an 
error. If it's an error (less than zero), ReadlSAM just 
goes back where it came from with RetumCode the same 
as what came from FINDEX( ) . If it's a legitimate record 
number instead, then the ISAMFile is accessed and a 
record read from RetumCode -1. The reason for the -1 
is that records are numbered in a Pascal file starting at 
zero, but we tend to think more logically when the first 
record is numbered "one". If this little irregularity is 
tolerated here, then all the rest of the logic can beUeve 
that the first record is #1, the second is #2, and so on. 

If the ISAM file isn't on the disk, the RetumCode is 
changed to -3 before control is retumed to the calling 
module, letting it know what the problem was. (A Retur- 
nCode of -2 from FINDEXO meant the key field wasn't 
found when the index was searched. This way, the 
original calling module can be coded to respond to 
whatever number of error conditions is necessary. ) 

WRITEISAMO 

WritelSAM is the procedure to write a record to the 
ISAM file. The parameters it needs are the file name and 
the key field. The only error condition that's anticipated 
here is the possible absence of this file from the disk, and 
that's not really an error— it just means we haven't writ- 
ten the first record yet. Thus the code here tries to 
RESET the ISAM file, and if that doesn't work it wiU 
REWRITE the file, starting it fix)m scratch. The same 
logic follows when the procedure writes the key field and 
record number to the .KEY file. If there's an error, the 
.KEY file hasn't beax started yet and it's handled the 
same way. 

Along with writing the record to the .KEY file, the 
same information is added to the index table arrays, af- 
ter incrementing MaxKeys appropriately. Thus, 
whenever a new record is written to the ISAM file the in- 
dex is updated in the .KEY file and in memory at the 
same time. The index table will remain valid without 
having to read the .KEY file into memory again. 

REWRITEISAMO 

RewritelSAM is very similar, but the differences are 
important. In this case an error that will need to be dealt 
with is very possible, so one of the parameters is again 



RetumCode. Since RewritelSAM is used to update a 
record, not write one in the first place, it is indeed a 
problem if the file doesn't exist on the dis'-.. Also, in this 
case we don't want to seek the end of the file and write a 
record there, we want to seek the position of the 
requested record and rewrite that same record. Remem- 
ber to subtract 1 from the record number— obtained from 
FINDEX( )— to account for records that start at zero. 

Having written all the code that's required to accom- 
plish these basic tasks, making the program do 
something useful is easy. The following procedures are 
the demonstrations, and I'll continue to point out ususual 
syntax and logic, but skip the simple stuff. 

READ DEMO 

Intended to be used in this program only, ReadDemo 
doesn't receive any parameters from the main logic 
which calls it, but it must pass some parameters to the 
procedures that it calls. First off, ReadDemo asks for the 
name that identifies the record to be read. Then it calls 
ReadlSAM to read the right record from the file, and 
displays the phone number to the CRT. Along the way it is 
prepared to deal with values of the parameter Retur- 
nCode that indicate the following problems in reading the 
file: 

Retum Code Problem 

-2 Key field not found when the index was 

searched. 
-3 The ISAM file didn't contain a record for 

that record number. 

(A retum code of -1 was used by LoadKeys to indicate 
that the .KEY file wasn't found. Though these errors 
could have been called -1 and -2, 1 prefer to associate 
certain RetumCode values with specific problems, so I 
don't usually re-use the same numbers, even in different 
procedures.) 

The statement "Read(Choice) ; " is used just to hold tt 
displayed phone number on the screen until the user e 
ters a RETURN. 

ADD DEMO 

Because all the nit-picky details are handled by th 
procedures that were coded earlier, this one to demoi 
strate adding a record to the ISAM file is very short an. 
sweet. It asks for the name (key field) and the i^ne 
number, then places them into the record for the ISAM 
file and writes it. Notice the section of code that starts out 
with the words "With ISAMRec Do". 

The problem that's possible when a record is added, of 
course, is that there niight be a duplicate of that key field 
in the index already. If we were to enter a phooe number 
for someone, forgetting that there was already an old and 
incorrect one there, the computer would never deliver 
unto us the correct phone number. Each time the index 
was searched and a matching key field found, it would 
point to the record containing the old number 

Therefore, the proper way to change a field is with the 
CHANGE feature, not by adding another record with the 
same key field. This procedure does a quick check of the 
index— using FINDEXO— to be sure that a key field 
doesn't ahready exist before a record is added to the file. 



34 The Computer Journal / Issue #22 

Count := 05 
With IndexRvc Do 
Begin 
Repeat 
Begin 

Read (IndexFile, IndexRec) ; 
Count : = Count + 1 ; 

KeyArayCCount] := KeyField; {load values from .KEY file into> 
Index Ar ay [Count 3 := RecNum; (arrays used for INDEX table > 
End; 
Until EOFdndexFile) ; 
End; 

MaxKeys := Fi leSize < IndexFi le) ; {determine how many records in file> 
Return: 

Clase( IndexFi le) ; 
End; 

Procedure Read ISAM (Fi 1 eNamelAnyFi le;ReadKey: Name; Var ReturnCode: Integer) ; 

Label Return; 

Begin 

Ret ur nCode : - F I NDE X ( ReadKey , Max Key s > ; 
If ReturnCode < then Goto Return; 
Assign < I SAMFile,FileName + '.ISA'); 
{♦I-> 

Reset <ISAIiFile> ; 
{«I + > 

If lOResult <> then 
Begin 

ReturnCode := -3; {file not found - bail out> 

6oto Return; 
End; 
Seek < I SAHFile, ReturnCode -1); {locate the right record> 
ReaddSAIiFile, ISAMRec) ; {read it, then close file> 

Close (ISAMFile); 
Return: 
End; 

Procedure WriteISAM<Fi leName: AnyFi le; I SAMKey : Name ) ; 

Label Return; 

Begin 

Assign<ISAMFile,FileName + '.ISA'); 

{«!-> 

Reset (ISAMFile); 
{♦I+J 

If lOResult <> then Re»»ri te < ISAMFi le) ; 
Seek(ISAMFile,FileSize(ISAMFile> ) ; 
Write< ISAMFile, ISAMRec) ; 
Assign ( IndexFi le,Fi leName + '.KEY'); 
{«!-} 

Reset (IndexFi le) ; 
{♦I + > 

If lOResult <> then Re»«-ite( IndexFi le) ; 
Seek ( IndexFi le,Fi I eSize(INDEXFile) ); 
MaxKeys :» MaxKeys -^ 1 ; 
With INDEXRec Do 
Begin 

KeyField := ISAMKey; 
RecNum := Fi leSize ( ISAMFi le) ; 
Write( IndexFi le, INDEXRec) ; 
KeyArayCMaxKeys3 := KeyField; 
IndexArayCMaxKeys3 := RecNum; 
End; 
Close (ISAMFile) ; 
CI ose( IndexFi le) ; 
Return: 
End; 

Procedure Re«riteISAM<Fi leName: AnyFi le; ISAMKey:Name;Var ReturnCode: Integer ) ; 
Label Return; 



The Computer Journal / Issue #22 



35 



Begin 

RsturnCode := 0; 
Assign<ISAMFiIe,FileName + '.ISA'); 

Reset (ISAMFile) ; 
{«! + > 

I^ lOResult <> then 
Begin 

ReturnCode := -1; {file not found 

Soto Return; 
End; 
Seek < ISAMFi le.FINDEX < ISAMkey.MaxKeys) -1 > ; 
WriteKISAMFile, ISAMRec) ; 
Return: 

ClosedSAMFile) ; 
End; 



bail out) 



Integer; 

to Read: 



Procedure ReadDeoo; 
Label Return; 
Var ReturnCode ; 
Begin 

WriteC^J'^J'^M, 'Enter Naaw to Read: '); 
Readln<Na«neIn) ; 

Read I SAM ('PHONE' , Naaein, ReturnCode) ; 
Case ReturnCode Of 
-2 : Begin 

kfc-itelnC-J^J^M, 'Error - KEY NOT FOUND IN INDEX'); 
Goto Return; 
End; 
-3 : Begin 

WritelnC-J^J'M, 'Error - RECORD NOT FOUND in ISAM FILE'); 
Goto Return; 
End; 
End; 
With ISAMRec Do Mr i teln ('^J'^J'-M, 'Phone Number: 
WriteC^J'^J'^M, 'Press <RETURN> to Continue... '); 
Return : 

Read (Choice) ; 
End; 



' , ISAMPhone) ; 



If a ReturnCode comes back that indicates the key wasn't 
found, it doesn't imply an error this time, it means 
everything's OK to proceed. Isn't it great the way we can 
use a function like that whenever it's needed! 

CHANGE DEMO 

ChangeDemo is very similar, but this one requires that 
a key field MUST exist before it's legitimate to continue. 
Obviously, it isn't possible to change a record that hasn't 
been written to the file yet, and any attempt to access a 
nonexistant record would certainly result in an 1/ error 
that would crash the program but good (attempt to seek 
beyond EOF). 

DELETE DEMO 

By now, this one last procedure needs little or no ex- 
plaining. It simply does a re-write of a record, replacing 
the phone number with a message that says "*** Deleted 
***". In actual practice on large computers, records are 
not really deleted physically from an ISAM file by an ap- 
plication program, but simply marked with a user- 
selected "delete character" in a user-selected position in 
the record. A system utility program is occasionally used 
that will put the file back into physically-sequential or- 
der, working in all the records that have been added, and 
leaving out the ones that were marked for deletion. 

Assuming that deleted records won't amount to enough 
disk space to cause problems, this procedure might be as 



far as you would want to go in your own applications. In 
fact, in some cases, it might even be an advantage to 
leave deleted keys in the index. In this program, for 
example, a phone number can be deleted if it turns out to 
be a wrong number— no point in continuing to use it— but 
then the deleted field can be replaced with the proper 
number at a later time by using the CHANGE feature. 

Closing Comments 

That's about all you might want to know about this 
program to simulate Indexed Sequential Access Files 
with your micro. If you're NOT a beginner, though, you 
may have spotted some possible improvements already, 
and I couldn't let you just sit there and smirk without 
pointing out that I, too, have thought of some. I'll take up 
just a little more room to point out one potential upgrade, 
and I welcome suggestions from anyone. This program is 
surprisingly fast and capable, but it can be made even 
more so at a cost of somewhat increased complexity. 

Binary Search 

If there are to be a limited number of records in the 
ISAM file, say, a couple of hundred friends' phone num- 
bers and addresses, a sequential search of the index 
array (such as in FINDEX) will be tolerably fast, and 
requires very little room in the program. If this principle 
is to be applied to an application program that will keep 
track of thousands of records, then it would be worth the 



36 The Computer Journal / Issue #22 

Procedure DeleteDemo; 

Label Return; 

VAR ReturnCode : Integer; 

Begin 

Write< -J' J^M, 'Enter Name to Delete: "); 
Read 1 n < Name In); 

1+ FINDEX<NameIn,Ha>:Keys> <0 then 
Begin 

Writeln< -J J~^M'Error - KEY NOT FOUND IN INDEX - Cannot DELETE'); 
Delay (3000) ; 
Goto Return; 
End; 

With ISAMRec Do 
Begin 

ISAMPhone := ' *«♦ Deleted •»♦'; 
Rewrite I SAM ('PHONE' , NameIn, ReturnCode) ; 
End; 
Return: 
End; 

{ A BEGIN like this, without a procedure or -function name, indicates the } 
{ start o-f the main program logic. The program actually starts here, and > 
< calls previousl y— coded procedures and -functions as needed. > 

Begi n 

LoadKeys ( 'Phone' , MaxKeys, ReturnCode) ; 
If (ReturnCode = -1) then 
Begi n 

Writeln ( 'Unable to locate KEY -file... returning to system.'); 
Goto Stop; 
End; 
Start: 

Write(#26' ISAM Phone File Example C Q=Quit R=Read A=Add D=Delete C=Change 

3 ' ) ; 

Read In (Choice) ; 

Choice := UpCase(Choice) ; 

Case Choice Of 

'Q' : Goto Stop; 

'A' : AddDemo; 

'R' : ReadDemo; 

'D' : DeleteDemo; 

'C : ChangeDemo; 
End; 

Goto Start; 
Stop: 
End. 

Procedure AddDemo; 
Label Return; 
Begin 

With ISAMRec Do 
Begin 

Write<'-J''J'~M, 'Enter Name To Add: '); 
Readln<I5AMName) ; 

I-f FINDEXdSAMNaaie, MaxKeys) >0 then 
Begin 

WritelnCJ-J'M, 'Error - DUPLICATE KEY - Cannot ADD '); 
Delay (3000); 
Goto Return; 
End; 
WriteC-J'J'-M, 'Enter Phone: '); 
Read 1 n ( I SAMPhone ) ; 
Write I SAM ('PHONE' , ISAMName) ; 
End; 
Return: 
End; 

Procedure ChangeDemo; 

Label Return; 

VAR ReturnCode : Integer; 



The Computer Journal / Issue #22 



37 



Begin 

WritBC^J-J-M, 'Enter Na«e: '); 
R«ad(Na«eIn) ; 

If FINDEX<Na<Mln,MaxKeys) <0 then 
Begin 

Writeln<-J-J-M, 'Error - RECORD NOT FOUND - Cannot CHANGE'); 
Del ay (3000); 
Goto Return; 
End; 
ReadlSAM < ' PHONE' , Naeeln , ReturnCode) : 
With ISAMRec Do 
Begin 

>fc'ite<^J'^J-M,'01d NuMber is: ' , ISAMPhone) ; 
WriteCJ'-J-'M, 'Enter NeM Number: '); 
Read < ISAMPhone) ; 

Re*<r i t e I SAM ( ' PHONE ' , Name I n , Ret ur nCode ) ; 
End; 
Return: 
End; 



extra programming cost to use a binary search of that in- 
dex instead. 

Actually, two major changes would be needed. The in- 
dex would always need to be sorted into ascending or 
descending order (based on the key fields),to use a 
binary search. This sort would have to be done each time 
a record is added to the file, before the index is accessed 
the next time. 

Second, the search itself would have to be re-written a 
Uttle. The details of all this are a little beyond this par- 
ticular article, but for those budding hackers who haven't 
already added the binary search to their bag of 
programming tricks, I'll give a few hints, at least. 

Begin by determining how many entries are in the 
array (MaxKeys, in this case). Assign a variable called 
FINISH the value in MaxKeys to start with, and initialize 
a variable called START to 1. Add START to FINISH and 
divide by 2 to find the middle of the array. Compare the 
value in the middle to what you're looking for, and see if it 
matches. If it does, the search is over alrea(fy. 

If it doesn't, determine whether the value you found is 
HIGHER or LOWER than the one you're looking for 
(that's why the array has to be sorted! ) . If it's higher, set 
FINISH to a value that's one less than the subscript you 
just checked. If it's lower, set START to one more than 
the subscript you just checked. Now, start over again 
with these new values for START and FINISH. Sooner or 
later, that middle element you check will be the one 
you're looking tor. 

It usually turns out that it's sooner than you expec- 
ted—a binary search is FAST. The reason is very simple 
(and you'll probably catch on real quick to why it's called 
what it is). After one comparis<ni, you're able to 
eliminate fully one-half of the possible elements as being 
either higher or lower than the one you're looking for. Af- 
ter the second comparis<Hi, you're able to eliminate half 
of the ones that were left. It turns out that it takes only 16 
comparisons (or fewer! ) to find an element among an 
array of 65,536 elements. Using a linear search, it would 
take— on average— 16 comparisons to find an element 
among an array of only 32 elements. 

In actual practice, you won't find yourself getting 
bored waiting for this program to find the right record 
number for any reasonable size index, and the binary 
search really shows its stuff the best whm the numbers 



are very large. On the other hand, a quick sort done only 
after adding a new record to the ISAM file doesn't add a 
lot of overhead, either. Just be sure to re-write the sorted 
index file as part of the EOJ (End Of Job) processing as 
you quit the program, so it won't have to be sorted again 
each time the program is used. After all, you might ac- 
cess a file thousands of times without adding new records 
to it, depending on the application. 

(By the way, a Quicksort is a real jewel in Pascal, 
using recursion. That might be a good subject for another 
article...) ■ 




"...received my moneyi \.Morth vvith /usf one 
issue..." 

— J. Trenbick 
■ always stop to read CTM. even though 
mast other magazines I receive land i-vrite for) 
only get cursory examination.. " 

— Fred BIcchman. K6UGT 



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(Continued from page 4) 

Still More On Soldering 
James O'Connor: 

I enjoyed your article in the Sep- 
tember/October issue. 

I think that soldering dates back to 
the Egyptians— for metals— and the 
appUcation to electrical circuits 
probably dates to Faraday and his 
contemporaties. Electronics is just a 
minor off-shoot of electrical 
engineering. 

Your differentiation between 
welding and soldering is a bit ex- 
treme. Most welding (not all) in- 
volves using a "welding rod" which 
is melted and flowed between the 
component parts to be joined. The 
rod usually melts at a lower tem- 
perature than the parts, like solder, 
but yes, the component parts melt 
too. 

On the other hand, metals when 
soldered do dissolve into the solder, 
a process which is similar to 
melting. When thin films of solder 
are used to join metals structurally 
(brazing), you will find that 
desoldering requires a higher tem- 
perature than the initial joining 
because of the change in com- 
position of the solder due to dissolved 
metals. The change is a couple hun- 
dred degrees in silver 
soldered/silver brazed stainless 
steel. 

This effect is not very noticeable in 
most electrical connection soldering 
because the quantity of solder used 
is so great, compared to the surface 
area of the joint, that the concen- 
tration of dissolved metal from the 
joined surfaces never gets very high. 
However, it does become noticeable 
at times, such as desoldering a DIP 
or socket from a board, where the 
pins are reasonably tight in the holes 
in the board AND the plating/con- 
ductor on the board lines the walls of 
all holes. 

Personally, I use a 7^2 watt iron 
for all my electronics work. I have a 
high power iron (15 watt) for use on 
heavy duty connections— 8 gauge 
wire to a lug on a transformer, etc. 

I'm surprised that you made no 
mention of the gallium and indium 
based special electronic solders. 
While the hobbiest isn't liable to use 
these, he should know that they 
exist, and that there are problems in 
trying to bond lead-tin to the 



The Computer Journal / Issue #22 



speciality solders or to parts "con- 
taminated" with them. 

In your review of "Sources", you 
might add a mention that Heath sells 
a kit for learning how to do elemen- 
tary electronic soldering— a board, 
parts, and instruction manual. That 
kit was my starting point and I still 
have the manual. 
Dave English 
Orange, CA 

Dave: 

Thanks for the comments, Dave. 
Actually the Egyptians were also the 
first to do VLSI (Very Large Scale 
Integration) they just happened to 
use large cut stones instead of logic 
gates. But seriously, I wanted to 
delineate welding from soldering 
because I have encountered novices 
who were sure that soldering was 
just a wimpy form of welding. The 
result of that misconception was a 
tendency to overheat connections in 
the belief that insufficient heat was 
the cause of their problems. In the 
old days welding and forming were 
done concurrently so that the high 
heat aided both processes, for 
example the gtin barrels of the 
famous Brown Bess muskets carried 
by Revolutionary War soldiers were 
formed and welded from a sheet of 
flat metal by means of the high tem- 
perature of the gunsmith's forge and 
a forming block. Today changes in 
shape would be a deformity so the 
welding rod which melts at a slightly 
lower temperature prevents that. As 
you correctly point out, it is still 
welding that occurs, but more on the 
surface than throughout the pieces. 
Supplying and controlling the 
precise amount of heat is very 
similar to soldering. 

Yes, indeed there is a chemical 
bond formed during soldering and it 
can affect the temperature required 
to de-solder a connection. For elec- 
tronics work my experience has 
been that this bond is not much of a 
problem if most of the residual 
solder can be removed. As you note 
there are situations where that is dif- 
ficult due to tight quarters. As as 
aside, this bonding effect is also 
present with chemical 'glues' and 
shows up dramatically in that most 
glues produce the strongest possible 
bond with the thinnest possible glue 
layer. So-called 'Super Glues' 
(cynoacrylate) exhibit this to the ex- 



The Computer Journal / Issue #22 

treme, remember the TV ad where a 
man is suspended from a beam with 
just one drop, if they had used two 
drops he might have fallen. This is 
directly opposite to the intuitive 
feeling that if a little is good then 
more is better. 

7Mi Watts! ! ! I had heard of such 
low power irons but had to check my 
catalogs to determine that, yes, they 
are available. Your successful use of 
them is testimony to the degree of 
proficiency you've developed. Size 
and shape of the iron's tip along with 
the wattage rating ultimately 
determine the tip's temperature so 
there is a wide range of suitable 
irons that can be used, stiU I would 
stick with the recommendations 
made in the article for anyone just 
getting into soldering. 

Specialty solders are used by 
people who do craft type 
metalworking and in industrial ap- 
plications but in my experience are 
very rare in electronics work. For- 
tunately, most articles that I have 
read about these solders do a good 
job of explaining where, when, why, 
what and how to use them and I en- 
deavored to model the series on elec- 
tronics soldering on this principle. 
The companies that sell these 
solders also provide good technical 
brochures about them. 

Good suggestion about the Heath 
Soldering Ck)urse, Catalog No. EI- 
3133 list price $19.95, I was not 
familiar with this particular course. 
Heath's educational courses are in- 
variably a good investment. In some 
respects the Soldering article and 
the two follow-on articles cover 
much the same material, so Com- 
puter Journal readers may want to 
use them as a psuedo course in 
soldering. Also, those familiar with 
Heath's kits will probably detect the 
fact that I diverge from and expand 
upon Heath's usual instructions 
about soldering. By all means, CJ 
readers should obtain a copy of 
Heath's catalog and feel confident 
about attempting any of the kits or 
educational products. 
James O'Connor 
Randolph, MA 



39 



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40 



The Computer Journal / Issue #22 



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P O. BOX 47«M, ATLANTA. GA 303(2 



Art: Your prompt response is very 
much appreciated. 

Good Grief! Looking at your back 
issue list is like finding buried 
treasure; what a kick. I'm enclosing 
a check for all the listed back issues 
and a two year subscription. 

May you prosper. 

Interests, Equipment, etc. We're 
principally Z-80, CP based. There 
are two homebrew units and an 
Ithaca Intersystems system with 
front panel. Also, have a little Z-8 
(Circia) and a yet-to-be-assembled 
MicroAce. There's a Godbout 68K 
system languishing in storage as a 
result of an abortive "bright idea"; 
the collapse of the oil business had 
much to do with it. I'm interested in 
wringing the maximum from the Z- 
80/S-lOO system and am looking for a 
reason (excuse?) to make a foray in- 
to 68K country. Am determined to 
know what goes on inside and look to 
your journal to aid and abate tje 
quest. 

Thanks. 
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Midland, TX 



Remax Drives 

BillKibler: 

I just read your column in the Sep- 
tember-October issue and im- 
mediately picked up on a comment 
about Remex disk drives. You 
referred to modified drives. I bought 
a couple of them and have had 
nothing but trouble. I used them on 
an AMPRO Little Board and found 
that it was almost impossible to 
verify a disk. I concluded that there 
was something sloppy about either 
the mechanics or the electronics or 
both, but didn't quite know what to 
do about it. 

Could you let me know what you 
did to modify the beasts? I enclose a 
SASE for a reply. I certainly will ap- 
preciate it. 

Frank Oechsli 

Richmond, CA 

Dear Frank: 

Thanks for the fan mail, and 
hopefully this information will get 
you going. Please send us any >fEW 
information you might get after 
playing with your drives. 

The Remex Disk drives that are 
currently available for as little as $39 



have many problems, but can be 
made useable. In the July- August 
issue of Computer Journal I covered 
several important solutions to the 
problems. Other magazines have 
also commented on some solutions 
(Micro Cornucopia #26) , which agree 
in part with my findings. These 
drives appear to be made rather 
marginally and without much 
quality control. A solution may in- 
volve one or more of the following : 

A) The 12 volt supply needs are 
much larger than most, and will ex- 
ceed the listed ratings. Limiting the 
number of drives per power supply, 
as well as adding more capacitance 
(2000ufd) has cured poor stepping 
problems. 

B) Problems with noise have been 
noted, and in one case shielding with 
steel helped. I found that adding 
more bypass caps (.022) can also 
improve their operation (the PC 
board doesn't have enough) . 

C) Precompensation has been 
noted as causing problems. Use 
125ns or none at all. The schematic 
shows some minor value changes in 
the read circuit design and I suspect 
the design is inadequate. Adjusting 
R27 can improve the operation, 
sometimes. PLEASE NOTE that 
most of my errors have been READ 
not WRITE errors. 

D) Several signals are fed directly 
off of the 12V line and without proper 
filtering will cause false write 
triggering and possible speed 
problems. Adding 0.01 and 10-20ufd 
across the input power socket can 
help. 

E) Speed regulation is controlled 
by an MJE210 and this device is in- 
sulated from the case by a mica 
washer. Excessively tightened 
screws will short this device and 
cause the drives to run full on 
(loosen screw) . I had one of the tran- 
sistors fail completely and replaced 
it. 

F) The guides or rails on which the 
head rides can become sticky and 
may need cleaning and (Hghtly) 
oiling. Head alingment has checked 
out good (usually), with only 
azimuth being occasionally off (play 
with rails to correct) . 

G) Check all mechanical and elec- 
trical connections as several units 
have had broken, loose, and poor 
connections. I found one loose wire 
on a motor unit and had to 



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It's the professional's word pro- 
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"recrimp" it. 

Remember, these units most 
likely have poor quality control, and 
any type of problem could be en- 
countered. The design appears to be 
minimum, and external help (larger 
and cleaner supply voltages) will be 
necessary. 

One of the most important points 
in fixing the problems with these 
drives is networking. This means 
talking and writing to others with 
bcih questions and solutions. Only 
through networking can both 
manufacturers and users keep 
poorly designed units either off the 
market or at least running. 

Best of luck. 
BiUKibler 
Sacramento, CA 



Reconsider TCJ's Emphasis 

Your letter seems to indicate an 
emphasis on robotics, real time data 
collection and process control, at the 
expense of "business" topics— yet 
your back issue topics suggest a 
much broader base. Please consider 
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are also required for practical ap- 
plications on the factory floor, and 
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micro multi-user operating systems, 
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42 



The Computer Journal / Issue #22 



The AMPRO Little Board Column 

by C. Thomas Hilton 



W^hether you are a hobbyist, or commercial 
developer, often the desire for a small, yet powerful, 
single board computer, (SBC), presents itself. Often the 
choice for a good SBC is between commercially available 
boards, or in-house manufacturing. This column will 
present my personal choice for many SBC requirements, 
the Ampro Series 100, or "Little Board® ," microcom- 
puter. Tliis system is no larger than a 5.25 inch disk drive, 
so it can be mounted in the drive enclosure, and it 
operates with very low current demands. 

The Little Board is available in a number of forms. It is 
available from Digital Research Computers as a kit, and 
in a number of different configurations from Ampro 
Computers. (See Figure One for vendor listing) . 

AMPRO Computers, Inc., 67 East Evelyn Avenue, 

Mountain View, CA 94039 (415) 962-0230. THE source for 

manuals, systems, and parts. 

Digital Research Computers Of Texas, POB 461565, 

Garland, TX 75046 (214) 225-2309. Little Board 

kits and ZRT terminal card. 

Integrand Research Corp., 8620 Roosevelt Ave., 

Visalia, CA 93291 (209) 651-1203 Cases, power supplies, 

and wiring harness. 

Colonial Data Services Corp., 80 Picket District Road, 

New Milford, CT 06776 (203) 355-3178. Disk drives 

and accessories. 

Figure 1 : AMPRO Series 100 and Little Board source list 



When considering SBCs for industrial, instnmien- 
tation, or other application, one must consider how he 
will develop the system. That is, what manner of 
"development system" is also required to use the board 
in question. I am using an Ampro Model 122 with my 
Kaypro 4-84 as a development system. The '122 is a dual 
48 track per inch, (48 tpi), microcomputer. It is a "ter- 
minal system." This means that it requires a terminal to 
communicate with it. I use the Kaypro as a "dumb" ter- 
minal for development of Ampro projects. 

The Little Board is a 64K, Z80, system capable of sup- 
porting up to four Double Sided, Double Density, (DSDD) 
disk drives with a standard Basic In/Out System, 
(BIOS), or up to 88 megabytes of hard-disk storage, with 
a modified bios. My Kaypro can handle only 10 
megabytes of hard-disk storage. With a terminal the Lit- 
tle Board is far more powerful, and versatile, in my 
opinion, than the Kaypro. In time, if Art allows me to con- 
tinue this column, we will explore the Little Board in 
great detail. At this point, however, we will assume that 
you are either looking for a well supported SBC, and have 
chosen the Ampro Series 100, or I have convinced you of 
how much computing enjoyment can be had with a Little 



Board. This column will begin with the assumption that 
you have either just received an Ampro Series 100, or Lit- 
tle Board. We will not repeat the material covered in this 
column. New Ampro users should be advised to obtain 
back issues of The Computer Journal to keep abreast of 
all projects. If reader interest warrants, user disks, with 
these articles and public domain software tools to per- 
form programming projects, will be made available. By 
providing public domain software tools, at reasonable 
acquisition costs, for use with this series, we will have 
some consistency. I will not hide from my readers. I will 
review reader contributions for this column, and answer 
any questions I receive, quickly, and personally. Though 
I have no connection with Ampro Computers, I feel my 
function is to assist you in the understanding of, and use 
of your Ampro SBC. 

The Ampro Series 100 systems have two serial ports, a 
printer port, and a disk expansion port. Owners of the 
"Little Board Plus" also have a SCSI port which can be 
used to interface to a hard disk and other devices. In this 
series we will deal primarily with the generic lA CPU 
card as found in the inexpensive Little Board kits, and 
Series 100 microsystems. 

Out of the box the Series 100 "Bookshelf Computer," 
the recommended development system, is ready to run 
once a terminal system has been prepared for its use. 
Most people interested in SBCs have a system that can be 
used as a terminal. Again, I use a Kaypro 4-84. In a like 
manner most people have an assortment of cables in 
reserve. I am a bit on the cheap side, and prefer to make 
my own cables. Constructing a cheap and simple cable 
will be the first project in this series. This is a bit 
pedestrian for you old salts, but there are a lot of begin- 
ners out there who need a little help as well. 

1. DB-25 RS 232-C Male Connectors, 2 each 

(Radio Shack #276-1547) 

2. Six Conductor Cable, (Or Ribbon Cable) 

(Radio Shack #278-722 is usable) 

3. Soldering Iron & Solder 

4. Small hand tools, tweezers, etc. 

Figure 2: Materials required. 



Cable Construction 

Assemble all of the materials noted in Figure two. 
Before we get too carried away, let's force ourselves to 
tolerate a little theory. The Ampro communicates with 
the terminal via RS 232-C ports. In normal operation 
"Port A" is the terminal port. This port is wired as "DaU 
Communications Equipment," (DCE). This is the format 
we will use in building the cable. The Ampro end of the 



The Computer Journal / Issue #22 

cable must be wired as DCE, but your specific terminal 
may require a "Data Terminal Equipment," (DTE), 
format. Standard communications cables consist of 25 
signal paths. Not all of these 25 lines of a standard cable 
are supported by the Ampro/Little Board. We need only 
six actual signal paths to get our system on-line : 

1. Data Input 

2. Data Output 

3. Data Terminal Ready 

4. Clear To Send 

5. Signal Ground 

6. Equipment Ground 

In the list above. Data Input refers to serial data being 
received by the Ampro from the terminal. Data output 
refers to serial data being sent to the terminal. Data 
Terminal Ready and Clear To Send are "hand-shaking" 
signals to assure that the terminal is listening when it 
should, and vice versa with the computer. The signal 
ground is the common return path for all data signals. 
The equipment ground path is generally used to shield the 
cable, and assure that both the terminal and computer 
are of equal electrical potential. 

In this construction project we will use an "A" to in- 
dicate the Ampro end of the cable. "K" will indicate the 
Kaypro end of the cable. 

A statement such as "K2" refers to the Kaypro end of 
the cable, pin number two. In a like manner a reference 
to "A20" would refer to the Ampro end of the cable, pin 
20. Place a mark in the space provided when you have 
completed each assembly sequence. 

Prepare your connectors and cable for assembly at this 
time, marking one end with an 'A' for AMPRO END and 
the other end with a 'K' for KAYPRO END. 

D 1 . Connect Kl to Al ( One conductor to the same pin on 
each end, starting on the Kaypro end. ) 

D 2. Connect A2 to K2 

a 3. Connect K3 to A3 

D 4. Connect AS to K5 ( pin K4 and A4 are not connected) 

D 5. Connect K6 to K8 (On Kaypro side ONLY, here we 
define the unused DCD input state as active) 

D 6. Connect K7 to A7 

n 7. Connect A20 to K20 

At this stage of the assembly only the following pins 
should be connected, all others should be left vacant, un- 
connected. 

Ampro End: 1,2,3,5,7,20 

Kaypro End: 1,2,3,5,6,7,8,20 

There are six connections on the Ampro end because 
there are two ground paths. While only one ground path 
needs to be used, we will use two. One is defined as 



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44 



The Computer Journal / Issue #22 



equipment ground, the other as signal ground. In both the 
Ampro and the Kaypro these lines are tied together. 
Later we may wish to use this cable on another terminal 
where the two ground systems are different, hence we 
use the extra wire now, to avoid problems later. 
The Kaypro has two extra connections as pin 6, signal 

g)wer path, ( +5 volts), is used to define the unused input 
CD, pin 8, to its active state. 

A good technician triple checks his work, even when he 
knows he has done the work properly. Triple check your 
connections now. 

D 8. If you are using metal connector shields AND your 
cable has a metal braid type shield around the wires, 
connect the braid to the metal shield. If you are uncer- 
tain, ignore this step. 

D 9. Insert the Kaypro end of the cable into the SERIAL 
DATA PORT in the rear of the Kaypro. Consult your 
Kaypro manuals if uncertain as to which connector this 
is. 

n 10. Insert the Ampro end of the cable into Serial Port 
'A' at the rear of the Ampro. Consult your Ampro 
manuals if uncertain of the port's location. 

Assuming all of your cable connections are correct, 
and you are proud of your work, aUowing no sloppy 
soldering, the assembly of your terminal cable is now 
complete. 

Going On Line: 

The Ampro Series 100, Serial Port 'A' is configured for 
9600 baud without hand shaking, as a default assignment. 
Nearly all of the Kaypro communications programs to be 
found do not support hand shaking, nor do the programs 
found in Kaypro support magazines. Hand shaking is 
very important in data communications. Without it 
characters will be lost in transmission and data tran- 
smission si>eed will have to be reduced in an attempt to 
achieve reliability. The next segment of this article will 
concern itself with a high speed, but simple "dumb" ter- 
minal program. 

Most Kaypro communications programs may not be 
used above 2400 baud. This is due to the programmer's 
assumption that higher speeds were not possible. In fact 
their programs did not implement the system's hand 
shaking facilities. KTERM may be run at 19200 baud. 
Higher speeds are possible, but the Kaypro CONFIG 
program only allows up to 19200 baud. This is more than 
fast enough to get the full power from your Ampro Series 
100 microcomputer. 

KTERM is available on disk preconfigured for easy in- 
stallation of the Ampro Series 100. Lacking that, compile 
the Turbo Pascal, Version 3.0, program shown in Figure 
3. Once you have assured that it has compiled properly, 
place it on a newly formatted, Kaypro disk. Add to this 
disk the Kaypro CONFIG program. From this point on- 
ward it is assumed that you have studied both the Kaypro 
and Ampro System Manuals. If you have not studied 
them, do so now. 

The Kaypro "Serial Data Port" is connected to a Serial 
In/Out processing chip, (SIO). This SIO is referred to as 



SIOl on the Kaypro Series 84 systems. SIOl, Channel 'A' 
is not supported by the Kaypro BIOS. It is, however, 
initialized on power-up as the keyboard uses Channel 'B' 
of this SIO. Our Program initializes Channel 'A' for its 
own use, without disturbing Channel 'B.' 

The Kaypro's default modem data transmission rate is 
300 baud. It will have to be changed to the rate of 9600 
baud. This will allow us to communicate with the Ampro, 
whose default data rate is 9600 baud, long enough to 
reconfigure the Ampro for higher data speeds. Use the 
Kaypro CONFIG program, option 'M,' to set the Kaypro 
for a 9600 baud default data transmission rate. Press the 
Kaypro RESET button to assert the changes by writing 
them onto the system tracks of your disk. 

Run KTERM. 

Insert the Ampro SYSTEM DISK into drive 'A' of the 
Ampro. With KTERM running, turn on the Ampro. The 
Ampro log-on message may not be displayed properly, 
but it should be readable. 

Enter CONFIG 

Use the AMPRO CONFIG program, option '6,' to con- 
figure Serial Port 'A' as follows : 

1.8 data bits 

2. 1 stop bit 

3. even parity 

4. 9600 baud 

5. with hand shaking 

When you have assured that the system is functioning 
properly you may increase the baud rate to 19200, though 
9600 is fast enough for most operations. 

Changing Baud Rates 

To increase the baud rate, or lower it, enter the Ampro 
CONFIG program and set the desired baud rate. Install 
the changes ON DISK only. Do not install the changes in 
memory or communications will be lost. Exit KTERM 
and use the KAYPRO CONFIG program to set the 
desired baud rate. Press RESET on the Kaypro, and en- 
ter KTERM. RESET the Ampro and you should be on-line 
again. 

The Terminal Program 

KTERM is a very simple program. It has no features 
whatsoever. I have often been using the Ampro and found 
myself changing disks in the Kaypro, instead of the Am- 
pro. This is the kind of terminal function I prefer. 
KTERM may be easily expanded to suit your own tastes. 

We begin our discussion of the Pascal program with the 
first functional Hne of code. The entry: 

{C-} 

is a Turbo Pascal specific compiler option which inhibits 
the interpretation of control characters by the program. 
This feature is a must. Without it the host computer 
would attempt to act upon any control characters input at 
the console. We want the Ampro to to be sent control 



The Computer Journal / Issue #22 45 

Figure 3 

HERMIT SOFTWARE 
Pascal Program Source File 

Program: KTERM 

Version: 1.0a 

Class : Public Domain Utility 

Author : C. Thomas Hilton 

Date: July 12th 1985 
Hardware Requirements: 



Program Comments: 



{«C-> 
type 



Kaypro 4-84 

Ampro Series 100, Model 122 



The maximum speed that knoMn Kaypro communications 
programs have been able to interface with the Ampro 122 ha 
been 2400 baud. 

This dumb terminal program corrects the de-fects of these 
programs by allowing the AMPRO 122 to communicate with a 
Kaypro 4-84 at 19200 baud, the maximum data transmission 
rate allowed by the Kaypro CONFIG program. 

Use the Kaypro CONFIG program to set the baud rate in the 
KTERM working disk as the default data rate. 

This program is in routine use, and shoMS no de-fects. See 
the main text of this Application Note for the ATV^RO 122 
configuration set by the AMPRO CONFIG program. 

Use the ~-9, (null control code), to exit the program. 
This is the only user command available, or needed for 
particular application. 



< Turn off control character interpretation by program 



warkstring-string[803| < define a utility variable > 

const < define program constants > 

txrdy-4» < transmitter buffer ei^ity mask value > 

rxrdy-lj t receiver buffer full mask value > 

dat«part-4; < SIO-1 'A' data I/O port assignment > 

status-6; { SIO-1 'A' control /status port assignment > 

DtrH«it»«o8; < 'Hey I'm Busy' DTR flag value > 

DtrRdy'«E8; { 'Ready When You Are' DTR flag value } 



finis: boolean; 
ch:char; 



< set system variables 



Functions ti Procedures > 



FUNCTION ReadSt at: boolean; < turns TRUE if character received } 

begin 

ReadStat:'< (portCstatus] and rxrdy) <>0> 
end; {of ReadSt at} 



46 



The Computer Journal / Issue #22 



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codes from the terminal, and to act upon them. Essen- 
tially we want the terminal program to make the Ampro 
appear as if it were the only system in use. 

Pascal TYPE and VARIABLE declarations, as shown 
in Figure 3, are generic, and need not t)e modified for 
systems other than the Kaypro. 

The program CONSTA^fT declarations, however, may 
be redefined for non-kaypro users, or owners of differing 
models. 

Function READSTAT does little more than determine 
the the status of the receiver register of the SIO. Function 
READCHAR polls READSTAT untU the SIO indicates 
that a character has been received. It will then input the 
character. A logical AND is performed to mask-off any 
parity bit. In some systems, and terminals, the parity bit 
may trigger graphics characters. 

Procedure INIT initializes the SIO (which the Kaypro 
ignores, save for setting the keyboard channel) for data 
communications. This set of code sets the data channel 
for our default data format of an 8 bit data word length, 1 
stop bit, and even parity. Consult a ZILOG manual for the 
actual meanings of the codes shown. The operation of the 
SIO is beyond the scope of this small program. 

Procedure WRITECHAR simply sends a keyboard 
character to the Ampro upon demand. Procedure CEN- 
TER centers the KTERM log-on message on the host 80 
column terminal. 

The main program organizes all of the above functions 
and procedures to perform the logical exchange of data 
between the two systems. This includes the setting and 
resetting of the hand shaking signals. A test is made for 
an escape character, control @, (^@). If the escape 
character is detected, as an input character from the 
keyboard, the program aborts to the operating system. 

KTERM is one of those simple programs that hardly 
rate a comment, but are found in constant use. I use it ex- 
clusively with the Ampro, and cannot function without it. 
Other programs have features that do not allow me to in- 
terface with the Ampro as if it were actually the host 
system. 

Configuring The System 

If you purchase a Series 100 system, you will receive 
T/MAKER* , ZCPR3* , the "FRIENDLY OPERATING 
ENVIRONMENT* ," and standard CP/M* 2.2 as a "sof- 
tware bundle." Those who elect for other configurations 
will have these bundled programs as options. The 
T/MAKER package is a powerful set of applications 
programs, in a single system. WordStar* is not included 
in the bundle as T/MAKER has its own word processing 
system. 

The Friendly system is configured with WordStar, 
( WS), cursor commands. T/Maker, uses a more standard 
approach. The CP/M version of TM is set to use cursor 
control codes which are compatible with the ADM 3-A 
terminal, and Kaypro computers. Three different sets of 
cursor commands is at best, frustrating, especially if 
your system has user definable keys, as does the Kaypro. 

There are two options, either change the TM editing 
codes, which is allowed by the system, to those of the 
operating environment, or change the control codes of the 
operating environment. As a WS user this was a hard 
decision for me to make, especially since I use two dif- 



The Computer Journal / Issue #22 



47 



FUNCTION ReadChar:char; { read a character from SIO when char 
begin 

repeat unti 1 (ReadStat ) ; 

ReadChar:=char (portCdataport3 and «7f ) 
end; {of ReadChar> 



arr I ves 



PROCEDURE Init? 
begin 

portCstatusJ : =«18; 
port t status] : =1 ; 
port C status 3 : =0; 
port C statusJ : =3; 
port C status ]:=«0El; 
port CstatusJ : =4; 
port t status] : =«47; 
port Cstatus] : =5; 
port C st atus 3 : =%0cB; 
end; <of Init > 



{ set SIO-1 'A' for program use 



reset Channel 'A' 

call SIO interrupt register 1 

disable interrupt functions 

call SIO receiver parameters register 3 

set for 8 data bits, enable receiver 

call SIO protocol register 4 

one stop bit, even parity, X16 clock 

call transmit parameter register 5 

set for 8 data bits, enable transmitter 

and set Data Terminal Ready, (DTR) 



PROCEDURE WriteChar<kc:char>; { send a character to Ampro 

{ because no human could ever type so fast that the Ampro Mould miss a 

{ character no output handshaking is supported in this program. Other 

{ uses might require a treatment similar to that shown below for output 

{ handshaking. 

begin 

repeat unti 1 <portCstatus] and txrdy) <>0; { is buffer empty'' 

^. ^°':*"***P°''*'^ :=ord(kc); { when buffer empty send character out 
end; <of WriteChar> 



PROCEDURE Center <S: htorkString) ; { general utility for log-on, log-off > 
var R: integer; w^ utt 

begin 

for R: = l to <80-Length<S) ) div 2 do WriteC '); 
writeln (S) ; 
end; < of center > 



B«gin Main Program 



begin 

'"^*» i Initialize SIO-1 'A' for our use 

clrscr; { begin log-on sequence for Kaypro screen only 

center ('Hermit Software" s' ) ; 

writeln; 

center CK-TERM Version 1.0a'); 

writeln; 

center CA Kaypro 4-84 / Ampro Series 100 Dumb Terminal Program'); 

center ('Released Into The Public Domain July 1985'); 

writeln; 

center ('Press -^ to Exit'); 

writeln; writeln; writeln; 

writeln ('System Ready'); writeln; { End of log-on sequence 

finis:«f*lse; { set initial boolean escape value 

repeat < begin main loop 

if (keypressed) then < has a key been pressed? 

begin 

read(kbd,ch); < get it if so } 

if (ch--~e) then finis :»true { if exit code then exit without > 

< sending to Ampro } 



else 



end; 



WriteChar (ch) ; 



< if valid character then send to Ampro > 



if (ReadStat) then { check to see if a character has been received > 
''*5in { ».t DTR BUSY flag line > 

port C status] : =»5; port Cstatus] : ^DtrWai t ; 

write (ReadChar); < print the character > 

port Cstatus]: -5; portC6]:=DtrRdy; < reset DTR for next character 
end; 

until (finis); { ^^ 'finis' turns TRUE comes here > 
writeln; writeln; writeln; 

writelnCExiting KTERM Have A Nice Day! '); < log-off mnsage > 

*"**• C termination > 



48 



The Computer Journal / Issue #22 



ferent computers on a daily basis. I chose to alter the 
operating environment codes. The size, and number of 
commands in the TM system made the choice a little 
easier. 

ZCPR3 has a portion of the system BIOS set aside for 
terminal control code definitions. We will discuss these 
stored terminal codes, and how to use them, in a later ar- 
ticle. If you are using a popular terminal, or computer as 
a terminal, installation is a simple matter. At the com- 
mand prompt enter : 

AO > TCSELECT MYTERM < RET > 

a menu of supported terminals will be displayed to select 
from. The "TC" in the command name stands for "ter- 
minal cap." This 'cap" is the set of terminal control 
codes stored in the system BIOS. The support for these 
terminals, and systems, are very generic in nature. I 
found that I received better performance from the 
system by installing ZCPR3 manuaUy, using the "TC- 
MAKE.COM" utUity. 

One of the very nice things about the Ampro systems is 
the fact that they may be adapted easily to most any kind 
of terminal, or display system. In my work for the 
visually impaired we have used a serial keyboard as the 
input device, and a voice sythesizer as the output device. 
While we made extensive BIOS modifications, the actual 
hardware interface took only moments to accomplish. 
Due to the wide range of devices that may be used as a 
terminal, specific installation discussion would be 
meaningless to most readers. Everyone would feel that 
their system was not covered. The Ampro documentation 
is well done, and guides the first time user through the in- 
stallation steps required for non- standard terminal 
systems. 

As TM is the only full featured text editor, (ED.COM is 
also provided), I do have a comment to make for those 
who will be using TM for programming. TM produces 
sterile ASCII code. Unlike some editors, who use flipped 
bits and other trash for system use, TM does not put its 
flags in the general text. It does have a quirk, however. 

TM has a maximum line length of 300 characters in a 
Ca»/M system, 400 for 16 bit systems. Yes, 300 characters ! 
The screen can scroll left and right, as well as up and 
down! An off-screen "first line" stores the user's tab set- 
tings. A wide number of assemblers and languages get 
very upset when the first thing they see in the program 
file is a line of 300 characters. This "tab line" is com- 
posed of nothing but spaces and tab characters. 

When installing TM answer NO to the question "Should 
TABs be stored with the file?" By placing the cursor on a 
line of text and entering <ESC> S <TAB> TM will 
record tab characters, for the current editing session 
from this "model line." As TM is the bundled editor with 
the Series 100 systems, I will provide a tab line for all 
programs. The tab line problem is offset by the ability to 
produce extremely high quality printed listings, and 
documents with T/Maker. 

For those who wish to leave the tab line in their text 
files, there is an option. When saving programs enter: 



at the "WHAT NEXT?" prompt. Remember that, like 
ZCPR3, TM allows command lines of up to 255 charac- 
ters. 

My only complaint with TM, other than having to learn 
new editing keystrokes, is the inability to execute a .COM 
file from the command line. Learning to use TM as a 
programming tool will be included in future articles as 
well. 

While I didn't get into very much "good stuff" this 
time, it is hoped that this information will help you to get 
your system fimctional. Between the time you read this, 
and the next issue of TCJ is published, make friends with 
your system. In this way you will be ready for the projec- 
ts to come. There is a great deal planned for the future. A 
new CCP, (console command processor), for a larger 
TPA, a voice output enhanced BIOS, and a close look at 
the schizoid 'E' drive which allows reading, writing and 
formatting of other system's disks, to name but a few. I 
didn't know where to start a column. So, I began at the 
beginning, and there is a great deal I would like to cover 
that I didn't even get close to this time. Of course, if you 
have a project you are interested in seeing covered here, 
let me know. This is your column, as em Ampro user. ■ 



• * * 

AMPRO User Support 

Tom and I are both impressed with the AMPRO Little 
Board and their Bookshelf 100 computer series, and we 
making a major user support effort for these systems. 

In addition to this series of articles (plus the NEW-DOS 
series which is aimed at the AMPRO), Tom is preparing 
an AMPRO user disk library of 25 to 30 DSDD disks. 
These disks will be distributed thru the TCJ office, and 
we will provide an on-line RBBS when we can obtain an 
additional phone line. New disks will be added to the 
library as the material is available. 

I am especiaUy interested in SCSI related software, 
and plan on establishing separate disk volimins for this 
topic. Any SCSI material (whether for the AMPRO or 
not) will be greatly appreciated. 



NOT ABS SAVE 



The Computer Journal / Issue *22 



49 



Editor 



(Continued from page 1) 
The SCSI Interface 

Interfacing to microcomputers 
has been hmited by the lack of a 
satisfactory high speed port. Most 
Centronics® ports are implemented 
as only a printer driver with eight 
lines for data output and a few lines 
of input for printer status. The RS- 
232 configuration dates back to the 
slow Teletype® days and is slow 
with a lot of non-standard implemen- 
tations, and the IEEE-488 doesn't 
really fill the needs of the micro 
market. The SCSI interface 
(originally SASI) was developed by 
Shugart as a high speed parallel in- 
terface for hard disks, and is being 
adopted by many manufacturers as 
a general interface. 

Almost every issue of the technical 
design magazines tell about new 
designs incorporating the SCSI inter- 
face, and you'll be dealing with it in 
the very near future. Some of the 
reported implementations are the 
expanded Macintosh from Apple, the 
next micro from IBM, and the Apple 
LaserWriter II (which has 8 Mbytes 
of RAM and ROM) . The Ampro little 
boards (both the Z-80 and the 80186 
versions) provide SCSIplus, which is 
one thing which makes these such 
great development systems. Star- 
ting with th^ issue we'll have a 
regular section on SCSI with 
technical information, applications, 
and product news. 

Communications, User Disks, Odds 
&Ends 

We finaUy have a 300/1200 baud 
modem running on MDM740 (the 
communications program came in- 
stalled an the Ampro), and can 
receive and send files over the 
phone. We would like to establish a 
bulletin board, but the phone com- 
pany can not provide a second line 
and we can't tie up the existing line. 
For now we prefer to receive articles 
on disk, but arrangements can be 
made to transfer by modem if you 
call by voice in the evening. Short 
messages and subscriptions by 
charge card can be left for Art 
Carlson on the Kalispell BBS (406) 
257-6117 during the hours of 6pm to 
Sam Monday through thursday, 6pm 
Friday to 11am Saturday, and all 
day on Sunday Mountain Time. 
These facilities are provided by The 



Computer Place and the storage is 
limited, so please don't abuse the 
privilage. Would it help if we had a 
BBS on line during the limited hours 
of 10pm to Sam mountain time until 
we can obtain a second line? Leave a 
message and let me know. 

Tom Hilton will be the librarian 
for CP/M user's disks in the Ampro 
5V4 inch DSDD format, and the or- 
ders will be filled from the TCJ of- 
fice. We'll be starting with about 25 
disks of general CP/M files, and will 
add more as they develop. These 
files can be provided on some ad- 
ditional formats on request. Watch 
for more details in the next issue. 

I've been plagued with erratic 
read and write errors on one set of 
Shugart 8008" single sided drives. 
They would almost always read and 
write OK on the outer tracks, but 
would frequently give problems on 
the tracks above about number 60. I 
checked the voltages, changed the 
head load pads, cleaned the heads, 
and tried different disks, but the 
problem would alway reappear. I 
finally tried the drives in another 
cabinet with a linear power supply, 
and they worked perfectly so I 



THE BEST 280 
ASSEMBLER ON 
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figured that there just had to be 
something wrong with the power 
supply. 

This is a very strange set up with a 
low height switching type power 
supply mounted directly beneath the 
drives, and I have to set the drives 
outside the case in order to get at the 
supply. I put my old Heath scope on 
the output to check for 60 cycle ripple 
(again), and it looked clean— but 
then I noticed that the line looked a 
little fuzzy. When I cranked up the 
intensity I could see that there was a 
lot of high frequency noise riding on 
the DC. I put 20,000 mfd on each of 
the outputs and the drives performed 
flawlessly while the drives were out 
of the case. After reassembling 
everything I still get occasional 
problems from RFI picked up by the 
drives or the wiring. I'll have to pull 
the supply and put it in a separate 
well shielded enclosure with filtered 
output or just replace it with a linear 
supply. 

It's httle things like this that drive 
you nuts! Share your experiences 
and problems with others, perhaps 
the Kalispell BBS will make it easier 
to communicate. 



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ASK WHY THEIRS ARE SO SLOW! 



'. . a breath of fresh air . ." 

Computer Language. Feb. 85 

". . in two words, I'd say speed & 
flexibility", 

Edward Joyce, User's Guide #J5 




Now fully compatible with M80 
in Z80 mode with many exten- 
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features. 

To order, or to find out more 
about our complete family of 
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(800) S33-3001, <412) 282-0864 
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Z90 CP^ compeiibtiity required 



50 



The Computer Journal / Issue #22 



The Magazine Marketplace 

Now Uiat Creative Computing and 
Popular Computing have ceased 
publishing, we need to think about 
what we want in a magazine. Who 
should support a magazine, the 
readers or the advertisers? Who 
should a magazine support, its 
readers or the advertisers? Are 
readers only necessary as numbers 
to justify high advertising rates? 

I have just received a mailing 
from Ziff-Davis Professional List 
Services offering to rent the mailing 
list for Creative Computing (which 
Ziff-Davis shut down last month), 
and they say that Creative Com- 
puting has (or rather had) 233,772 
subscribers. If my memory serves 
me right, one of the other magazines 
had over 500,000 subscribers when 
they shut down. These magazines all 
gave the same reason for 
folding— falling advertising income. 
It didn't matter that they had 
several hundred thousand sub- 
scribers—advertising dollars were 
what kept them open. 

You would think that the subscrip- 
tions from a half-million readers 
should be enough to support a 
magazine without ANY advertisers, 
but producing a slick magazine with 
lots of four color illustrations is very 
expensive. Magazine rack sales are 
another drain. I have seen audited 
reports which stated that 60% of the 
magazines sent to the magazine 
racks were unsold and sent to the 



shredders. The specifics in one case 
were 90+ thousand sent out and 60+ 
thousand shredded for that month. 
Someone has to pay for the 60,000 
magazines turned into scrap 
paper— and it isn't the subscriber. 

Everthing seems to cost too much, 
and subscriptions to the better 
magazines are not cheap, but in 
many cases the price of a subscrip- 
tion does not even cover the cost of 
printing and mailing the issues— and 
I understand that when subscrip- 
tions are placed through the national 
subscription agencies all of the 
money may go to the agency without 
one penny to the publisher. We sub- 
scribers have come to expect large, 
slick, four-color magazines at low 
cost, or even below cost, subscrip- 
tion fees. Then we complain about 
the large percentage of advertising 
(up to 75% of the space) and the 
weak editorial content! As Frank 
said in issue 402 of Echelon's Z-News 
"Many computer magazine editors 
have little or no investment in or 
emotion for our industry or its har- 
dware... You seldom notice jmything 
written that offends anyone; you 
notice they remind of melba 
toast... Remember, their revenue 
comes mainly from advertisers, not 
from you their readers." It is ob- 
vious that if profit and continued 
existence depend on the advertisers, 
then the readers will be treated 
merely as numbers to justify high 
advertising rates— and the subscrip- 




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tion rates will have to very low to at- 
tract large numbers of readers who 
don't gain much from the magazine. 
I know that I've subscribed to 
magazines which didn't have much 
useful content, but they were so thick 
and cheap that it seemed a bargain. 

We publish TCJ for the readers, 
and limit the advertising to products 
that we feel our readers should know 
about. The limited funds restrict the 
amount of promotion we can afford, 
and we can't pay the authors as 
much as we would like, but we are 
free to publish what our readers 
want without worrying about offen- 
ding any advertisers. If you like an 
article, write the author and let him 
know, because they aren't doing it to 
get rich but rather because they 
want the information published ! ■ 



Registered Trademarks 

It is easy to get in the habit of using 
company trademarks as generic terms, 
but these registered trademarks are 
the property of the respective com- 
panies. It is important to acknowledge 
these trademarks as their property to 
avoid their losing the rights and the 
term becoming public property. The 
following frequently used marks are 
acknowledged, and we apologize for 
any we have overlooked. 

Apple n, II + , lie, He, Macintosch, 
DOS 3.3, ProDOS; Apple Computer 
Company. CP/M, DDT, ASM, STAT, 
PIP; Digital Research. MBASIC; 
Microsoft. Wordstar; MicroPro Inter- 
national Corp. IBM-PC, XT, and AT; 
IBM Corporation. Z-80. Zilog. MT- 
BASIC, Softaid, Inc. Turbo Pascal, 
Borland International. 

Where these terms (and others) are 
used in The Computer Journal they are 
acknowledged to be the property of the 
respective companies even if not 
specifically mentioned in each occuren- 
ce. 



The Computer Journal / Issue #22 



51 



Mew Products 



Bootable Z-System for H89/90 

Analytical Products offers a 
Bootable Z-System disk for Heath 
and Zenith models 89 and 90 
machines with no installation 
required. Just place the disk in the 
drive and press reset and the full Z- 
System, completely replacing 
CP/M, is up and running. The price 
for the bootable disk is $98.00 plus 
$3.00 shipping and handling. Source 
code for ZCPR3 and its utilities, and 
utilities of ZRDOS are also available 
at additional cost. The ready-to-run 
H89/90 Z-System can be ordered 
from Analytical Products, 20663 
Avenue 352, Woodlake, CA 93286, or 
call Mr. Peter Shkabara at (209) 564- 
3687 for literature and more infor- 
mation on Heath and Zenith produc- 
ts. 



Amiga-Lint C Diagnostic Facility 

Gimple Software announced their 
Amiga-Lint, a diagnostic facility for 
the C programming language, run- 
ning on the Commodore Amiga. 
They state that Amiga-Lint will 
analyze C programs and report on 
bugs, glitches and inconsistencies, in 
effect, providing a strong typing 
facility for C. Amiga-Lint looks 
across multiple modules and so en- 
joys a perspective that a compiler 
doesn't have. It aids considerably in 
developing reliable programs and in 
porting programs from other 
machines and operating systems. 
Amiga-Lint resembles the Lint that 
runs on the UNIX O.S. but has more 
feature and is better tuned to the 
68000 environment. 

Among the many errors reported 
on by Amiga-Lint are: type incon- 
sistencies across modules, 
parameter-argiunent mismatches, 
library usage irregularities, 
uninitialized variables, value-return 
inconsistencies, variables declared 
but not used, suspicious use of 
operators and unreachable code. 
Amiga-Lint has many features, in- 
cluding fuU K&R support, one-pass 
very fast operation, no fixed-size 
tables to overflow, configurable to 



arbitrary architectures and special 
Lint-style comments to suppress 
errors. Amiga-Lint is delivered with 
user-modifiable standard library 
descriptions for several C compilers. 
Amiga-Lint runs under Amiga's 
CLI interface. It will use all the 
memory available. Amiga-Lint is 
available for the special introduc- 
tory price of $98.00, including ship- 
ping within the continental U.S. 
directly from Gimple Software, 3207 
Hogarth Lane, Collegeville, PA 19426 
(215) 584-4261. 



CP/M-80 Emulation for MS-DOS 

The ICU Group has annoimced 
CP/EM-CP/M 80 Emulation which 
they claim gives IBM PC/XT/ AT 
and compatible computers the 
ability to run thousands of CP/M 80 
programs without the expense of ad- 
ditional coprocessor boards. 

CP/EM efficiently emulates the 
CP/M 8060 and Z80 environments on 
an MS-DOS based personal com- 
puter. CP/EM allows MS-DOS 
redirection of input and output 
devices used to alter device assign- 
ment allowing CP/M access to all 
standard MS-DOS devices and any 
installed device drivers. CP/EM 
uses the standard MS-DOS file 
system allowing data files to be 
shared between CP/M and MS-DOS 
applications. The (Command Interr- 
preter provides aU of the standard 
conunands provided by the CP/M 
console command processor. 

CP/EM version 1.2 provides ter- 
minal emulations for the Kaypro 10, 
ADM 3A/5 and Televideo 950. Serial 
conununications programs are in- 
cluded with CP/EM to aid in the 
transfer of programs and data bet- 
ween the CP/M and MS-DOS com- 
puters. CP/EM runs on any MS- 
DOS, version 2.0 or later, based per- 
sonal computer with at least 32K of 
memory available for application 
programs. 

CP/EM can be ordered from The 
ICU Group, PO Box 10118, 
Rochester, NY 14610 (716) 425-2519 



DOS 3.3 Compatibility with Apple's 
800K UnlDisk 

Apple Computer's new 800K 
UniDOS 3.5 drive gives five times the 
storage capacity of floppy disks, but 
no program support for Apple's DOS 
3.3 operating system. 

MicroSPARC's new UniDOS 3.3 
operating system fills this gap for 
programs and data files that exist 
under DOS 3.3 by providing big 800K 
disk capacity and complete Ap- 
plesoft compatibility with Apple's 
DOS 3.3. 

Key UniDOS features are: (1) Two 
400K volumes per disk; (2) Supports 
up to two UniDisk 3.5 drives ad- 
dressable as drives 1-4; (3) Allows 
intermixing 5.25 inch and 3.5 inch 
drives; (4) Allows up to 217 catalog 
names per disk; (5) Uses only IK of 
user memory (in addition to normal 
DOS 3.3 memory space) . 

UniDOS 3.3 comes with a user 
manual and Technical Data Sheet 
showing the modified DOS 3.3 ad- 
dress for systems progranrniing. It 
runs on the Apple II Plus, Apple He, 
and Apple lie, smd software 
developer licenses are available. 

UniDOS 3.3 is available for $49.95 
postpaid from MicroSparc Inc., 45 
Winthrop Street, Concord, MA 01742 
(617) 371-1660 



MasterFORTH Supports 8087 

MicroMotion MasterFORTH 1.2 
for the IBM PC family now supports 
the 8067/80287 math co-processor. 
This 8067 extension includes a com- 
plete macro assembler with local 
labels supporting all precisions, op- 
codes, and synchronization. The 
floating-point package includes a full 
complement of transcendental and 
high-level functions, as well as for- 
matted input and output routines. 
Both the assembler and the floating- 
point package are provided as sour- 
ce files and as relocatable overlays. 
A software version of this package, 
which completely matches the har- 
dware version, is also available. Ap- 
plications can test for the presence 
( Continued on page S4) 



52 



The Computer Journal / Issue #22 



Back Issues Available: 



Volum* 1. Ntimbcr 1 (Ittu* #1): 

• The BS-232C Serial Interface, Part One 

• Telecomputing with the AppleU: Tran- 
sferring Binary Files 

• Beginner s Column, Part One: Getting 
Started 

• Build an "Epram" 

Volum* 1. Number 2 (Issua »2): 

• File Transfer Programs for CPIM 

• The RS232C Serial Interface, Part Two 

• Build a Hardware Print Spooler, Part 
One: Background and Design 

• A Review of Floppy Disk Formats 

• Sending Morse Code With an Apple][ 

• Beginner's Column, Part Two: Basic 
Concepts and Formulas in Electronics 

Voluma 1 , Number 3 (Issue #3): 

• Add an 8087 Math Chip to Your Dual 
Processor Board 

• Build an AID Converter for the AppleU 

• ASCII Reference Chart 

• Modems for Micros 

• The CPIM Operating System 

• Build a Hardware Print Spooler, Part 
Two: Construction 

Volume 1. Number 4 (Issue #4): 

• Optoelectronics, Part One: Detecting, 
Generating, and Using Light In Electronics 

• Multi-user: An Introduction 

• Making the CPIM User Function More 
Useful 

• Build a Hardware Print Spooler, Part 
Three: Enhancements 

• Beginner's CoUmn, Part Three: Power 
Supply Design 

Volume 2, Number 1 (Issue #5): 

• Optoelectronics, Part Two: Practical 
Applications 

• Multi-user: Multi-Processor Systems 

• True RMS Measurements 

• Gemini- 10X: Modifications to Allow 
both Serial and Parallel Operation 

Volume 2, Number 2 (Issue #6): 

• Build a High Resolution S-100 Graphics 
Board, Part One: Video Displays 

• System Integration, Part One: Selecting 
System Components 

• Optoelectronics, Part Three: Fiber Op- 
tics 

• Controlling DC Motors 

• Multi-User: Local Area Networks 

• DC Motor Applications 

Volume 2, Number 3 (Issue #7): 

• Heuristic Search in Hi-Q 

• Build a High-Resolution S- 100 Graphics 
Board, Part Two: Theory of Operation 

• Multi-user: Etherseries 

• System Integration, Part Two: Disk Con- 
trollers and CPIM 2.2 System Generation 



Volume 2, Number 4 (Issue #8): 

• Build a VIC-20 EPROM Programmer 

• Multi-user: CP/Net 

• Build a High-Resolution S- 100 Graphics 
Board, Part Three: Construction 

• System Integration, Part Three: CPIM 
3.0 

• Linear Optimization with Micros 

• LSTTL Reference Chart 

Volume 2, Number S (Issue #9): 

• Threaded Interpretive Language, Part 
One: Introduction and Elementary 
Routines 

• Interfacing Tips and Troubles: DC to DC 
Converters 

• Multi-user: C-NET 

• Reading PCDOS Diskettes with the 
Morrow Micro Decision 

• LSTTL Reference Chart 

• DOS Wars 

• Build a Code Photoreader 

Volume 2, Number 6 (Issue #10): 

• The FORTH Language: A Learner's Per- 
spective 

• An Affordable Graphics Tablet for the 
Apple ][ 

• Interfacing Tips and Troubles: Noise 
Problems, Part One 

• LSTTL Reference Chart 

• Multi-user: Some Generic Components 
and Techniques 

• Write Your Own Threaded Language, 
Part Two: Input-Output Routines and Dic- 
tionary Management 

• Make a Simple TTL Logic Tester 

Volume 2, Number 7 (Issue #11): 

• Putting the CPIM lOBYTE To Work 

• Write Your Own Threaded Language, 
Part Three: Secondary Words 

• Interfacing Tips and Troubles: Noise 
Problems, Part Two 

• Build a 68008 CPU Board For the S-100 
Bus 

• Writing and Evaluating Documentation 

• Electronic Dial Indicator: A Reader 
Design Project 

Volume 2, Number 8 (lesue #1 2): 

• Tricks of the Trade: Installing New I/O 
Drivers in a BIOS 

• Write Your Own Threaded Language, 
Part Four: Conclusion 

• Interfacing Tips and Troubles: Noise 
Problems, Part Three 

• Multi-user: Cables and Topology 

• LSTTL Reference Chart 

Volume 2, Number 9 (Issue #1 3): 

• Controlling the Apple Disk ][ Stepper 
Motor 

• Interfacing Tips and Troubles: Inter- 
facing the Sinclair Computers, Part One 



• RPM vs ZCPR: A Comparison of Two 
CPIM Enhancements 

• AC Circuit Anaysis on a Micro 

• BASE: Part One in a Series on How to 
Design and Write Your Own Database 

• Understanding System Design: CPU, 
Memory, and I/O 

l»»u» Number 14: 

• Hardware Tricks 

• Controlling the Hayes Micromodem II 
From Assembly Language 

• S-100 8 to 16 Bit RAM Conversion 

• Time-Frequency Domain Analysis 

• BASE: Part Two 

• Interfacing Tips and Troubles: Inter- 
facing the Sinclair Computers, Part Two 

/ssue Number 15: 

• Interfacing the 6522 to the Apple ]l and 
He 

• Interfacing Tips and Troubles: Building 
a Poor-Men's Logic Analyzer 

• Controlling the Hayes Micromodem II 
From Assembly Language, Part Two 

• The State of the Industry 

• Lowering Power Consumption in 8" 
Floppy Disk Drives 

• BASE: Part Three 

Itaue Number 16: 

• Debugging 8087 Code 

• Using the Apple Game Port 

• BASE: Part Four 

• Using the S-100 Bus and the 68008 CPU 

• Interfacing Tips and Troubles: Build a 
"Jellybean" Logic-to-RS232 Converter 

lB9ut Number 17: 

• Poor Man's Distributed Processing 

• Base: Part Five 

• FAX-64:Facsimile Pictures on a Micro 

• The Computer Corner 

• Interfacing Tips and Troubles: Memory 
Mapped 110 on the ZX81 



laaue Number 18: 

• Interfacing the Apple II: Parallel 
interface for the game port. 

• The Hacker's MAC: A letter 
from Lee Felsenstein 

• S-100 Graphics Screen Dump 

• The LS-100 Disk Simulator Kit: A 
product review. 

• BASE: Part Six 

• Interfacing Tips & Troubles: 
Communicating with Telephone 
Tone Control 

• The Computer Corner 



The Computer Journal / Issue #22 



53 



IMU* Number 19: 

• Using The Extensibility of FORTH 

• Extended CBIOS 

• A $500 Superbrain Computer 

• Base: Part Seven 

• Interfacing Tips & Troubles: Part Two 
Communicating with Telephone 
Tone Control 

• Multitasking and Windows with CP/M: 
A review of MTBASIC 

• The Computer Corner 



Issue Number 20: 

• Build the Circuit Designer 1 MPB: 
Designing a 803S SBC 

• Using Apple II Graphics from CP/M: 
Turbo Pascal Controls Apple Graphics 

• Soldering and Other Strange Tales 

• Build a S-100 Floppy Disk Controller: 
WD2797 Controller for CP/M 68K 

• The Computer Corner 



IiiM Nnmber 21: 

• Extending Turbo Pascml: Customize with 
Procedures and Functions 

• Unsoldering: The Arcane Art 

• Analog Data Acquisition and Control- 
Connecting Your Computer to the Real 
World 

• BuUd the Circuit Designer 1 MPB: Part 2 - 
Programming the 803S SBC 

• The Computer Corner 



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54 



The Computer Journal / Issue #22 



Advertiser's Index 

Alliance Computers 12 

AMPRO Computers 8, 43 

Apropos 24 

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Barnes Research 40 

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John Bell 54 

Bersearch 9 

Blankenship Basic 40 

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Classifieds 53 

Computer Trader 37 

Digital Images 46 

Echelon, Inc 4, 29 

Intellicomp 19 

Jerryco 20 

Miller Microcomputer Services. . . 41 

Micro Systems Research 24 

Next Generation Systems 26 

Poor Person Software 15 

Public Domain Software. 54 

Remote Measurement 38 

SLR Systems 49 

Softaid 31 



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Artie Technologies announces the 
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SynPhonix 200-VIP retails for $295 
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8344 



The Computer Journal / Issue *22 



55 



Computer Comer 



32 Bit System Bus 

On a different note, I would like to 
propose a new standard for using 32 
bit systems. One of the topics of con- 
siderable discussion is how to handle 
the new 32 bit wide data structures. 
For the hobbyist it is a real problem 
of cost versus speed. Most new 
systems are being designed as stan- 
dalone units which do not use a bus 
system. This idea doesn't make use 
of a hobbyist's already existing sup- 
ply of computer stuff. In my case, I 
have quite a few S-100 boards and 
would like a system that used them. 
Currently, S-lOO will handle 16 bits 
by multiplexing the data bus after 
flagging a sixteen bit move. S-100 
also has some known speed limits, 
abour 10 to 12 MHz at present. 

I find the speed and use of the six- 
teen bit flag an acceptable solution, 
but the bus doesn't have room for 
more data lines. My proposal is to 
use two S-100 buses, side by side. The 
32 bit only card would be a double 
width S-100 card. This would require 
a standard spacing between the bus 
systems but for 32 bits that's OK. 
TTiis newer use of the extra S-100 bus 
would not have to be the standard 
pinout. However, if the same pinout 
was used on both buses it would 
make it possible to use the same 
memory cards in each side for 16 or 
32 bit wide data. The use of different 
S-100 pinouts on the other hand, 
allows for some special functions 
and signals not now supported by the 
standard. 

Another option to the use of two 
buses side by side would be splitting 
a 22 slotter in half, by cutting all the 
traces (except power and ground) at 
the half way point. A special 32 bit 
master card would be two separate 
cards connected together (by cable 
or socket connection) that spanned 
the cut traces. In either case, the 
signals and pinouts could either be 
the same or different, depending on 
the standard developed. I know that 
Viasyn was looking for a way to han- 
dle preregulated power supply 
signals, and this could also be han- 
dled with two different buses. 

This concept isn't new, as several 
of the big boys already have systems 
in which a standard number of pins 
is used, but the number of sockets 
per card varies depending on how 



;NO OPS TO HELP SET THINGS UP RISHT 

;LOAD NUMBER OF SECTORS IN D REGISTER 

;ADDRESS TO START WRITING TRA K DATA TO 

;LOAD A WITH DRIVE B NUMBER AND DENSITY 

; OUTPUT A TO DISK CHIP, SELECT DRIVE 

; TAKE CONTROL AND STOP ANY INTERRUPTS 

;SET UP LOOP COUNT VALUES 

;DATA PORT ADDRESS IN C FOR INDIR 

;DISK CHIPS FULL TRACK COMTV^D 

; TELL DISK CHIP READ A FULL TRACK NOW 

SHAIT A FEW CLOCK CYCLES 

;WAIT SOME MORE FOR CHIP TO GET DATA 

; Z80 GET DATA FROM I/O AND WRITE TO HL 

; COUNT DOWN ON LOOP COUNTER 

; ST ILL LOOPING SO BACK AND SET MORE 

;GET BACK TO DDT PROMPT. 



USE Q9000 TO RUN PROGRAM. MUST BE ON DESIRED TRACK FIRST 
9008 WILL CHANGE FOR DIFFERENT DRIVES AND DENSITY. CHECK 
BOO*. FIRST AND WATCH OUT FOR INVERTED LOGIC. 



TYPICAL ID MARK OF FORMATTED DISK 

FF FF FF 00 00 00 00 00 00 FE 02 00 14 00 C3 2D FF FF FF FF FF 



9000 


00 


00 




NOP 


NOP 


9002 


16 


lA 




MVI 


D, lAH 


9004 


21 


00 


01 


LXI 


HL , 1 00H 


91307 


3E 


2D 




MVI 


A, 7D 


9009 


D3 


63 




OUT 


63 


990B 


F3 






DI 




900C 


06 


00 




MVI 


B,00 


900E 


0E 


67 




MVI 


C,67 


9010 


3E 


E4 




MVI 


A, 34H 


9012 


D3 


64 




OUT 


64 


9014 


18 


00 




J MP 


R,0 


9016 


IB 


00 




J MP 


R,0 


9018 


ED 


B2 




INIR 


90IA 


15 






DCR 


D 


901B 


C2 


0C 


90 


JNZ 


900C 


901E 


FF 


FF 


FF 


RST 


7 



CRC 
SECTOR LENGTH 
SECTOR NUMBER 
SIDE NUMBER 
TRACK NUMBER 
THIS TELLS CONTROLLER ID FOLLOWS 



many hardware extensions are 
needed to handle the project. What is 
missing from the other ways, which 
the S-100 would provide, is the cost of 
this solution. This solution makes 
use of the already existing supply of 
8 and 16 bit boards, disk controllers 
and I/O cards. Most 32 or 16 bit 
systems still write/read the disk in 8 
bits and do their I/O in 8 bits, which 
leaves only memory, graphics, and 
CPU functions needing a larger data 
path. 

A project then for the future will be 
a 68020, doing 16 bit data transfers. 
The CPU will be spread over two 
cards for using two halves of a 22 slot 
bus. Regular 8 bit memory and I/O 
cards will be in either half, only the 
data path will be split, lower 8 bits in 
front, upper in back. The need for 
such a system would be fast 16 bit 
wide video mapping, and this video 
would make up the other half of the 
CPU card. The 24 bit S-100 address 
would be the same for front and 
back, allowing generic cards to be 
used throughout. 

The operating system for the 
above would be FORTH, and my 
project on putting FORTH in ROM is 
still moving along. A few good books 
for understanding FORTH are : 

Threaded Interpretive 

Languages by R.G. Loelinger, 
BYTE Books. This book discusses 
how a FORTH type system is 



designed and implemented. The 
sample is a Z-80 FORTH. A good 
book for those who want to know 
more, somewhat entertaining, 
also. 

Inside F83 by C.H. Ting Phd, 
OFFETE Enterprises, Inc. For 
those using FORTH 83 this book is 
a must. I was stumbling along until 
I got it. The introduction and 
details will answer almost all 
possible questions. 

Don't forget the traditional sources 
for help on FORTH: 
FORTH INTEREST GROUP, PO 
Box 8231, San Jose, CA 95155. They 
publish FORTH DIMENSIONS 
which is included with the $15 
membership fee. 

MOUNTAIN VIEW PRESS, INC.. 
PO Box 4656, Mountain View, CA 
94040. These people were the 
origin] publisher of FORTH 
Dimensions, but now are strictly a 
resource center for FORTH 
publications. 

To see and read about some dif- 
ferent applications try one of the 
special group publications such as 
FORML Proceedings and The 
Rochester Proceedings, or The 
Journal of Forth Applications and 
Research. I got a couple of these 
books and found some interesting 
stuff. The degree of help is limited 
however as these were papers 
presented at conferences. ■ 



56 



The Computer Journal / Issue #22 



THE COMPUTER CORMER 

A Column by Bill KIbler 



oeveral things have happened 
recently to cause me to review some 
disk format fundamentals. It seems 
that most people have some idea 
about how disks are formatted and 
used, but some misconceptions 
abound about a few simple but im- 
portant concepts. What must be kept 
in mind when dealing with dissimilar 
formats are the software and har- 
dware parameters. The hardware 
part is how your computer's disk 
controller formats, writes, and reads 
disks. The software part is the 
tricking of hardware to read or write 
unusual formats. 

Let's review things by looking at 
standard eight inch disks, using the 
single density format called IBM 
3740. This single density 
arrangement was established way 
back in the beginning and is the only 
true standard of any disk format. 
The disk has 26 sectors of 128 bytes of 
data and plenty of overhead infor- 
mation. It is this overhead infor- 
mation that can cause some trouble 
with varied formats. The disk con- 
troller will check the "ID marks" (a 
part of the overhead) to find out if it 
is on the right track, and then find 
the correct sector. Other infor- 
mation in the ID is the sector size 
(00=80h, 01=100h bytes) and a CRC 
flag. A good way to see what a 
proper disk format is, is to do a full 
track read. I have supplied a simple 
listing that will allow the SDSystems 
Versa Floppy II to read a full track 
(read the comments and change for 
other systems). My procedure is to 
use SID (or DDT) and clear memory 
to A(XX)h and assemble the listing at 
9000h. This allows you to exit SID, 
change tracks or whatever, and 
return to SID to reread a new track. 

Now that you have seen a full 
track, what do you look for if this is a 
disk you have been unable to read? I 
look first for the order of sectors, are 
they in sequence or skewed? 
Skewing is done to get more sectors 
read during each rotation of the disk. 
Disk read time is not fast enough to 



read one sector after the other. The 
delay needed to change pointers and 
set registers for the next read, is 
usually enough that a skew of six 
(skipping five sectors and reading 
the sixth) works fine. This is part of 
the standard and will be handled in 
most BIOSs. Some systems however 
do it during formatting and will need 
the BIOS's skew turned off. 

This is actually one of the points of 
this whole discussion, as most people 
have trouble understanding the dif- 
ferences. Looking at a directory 
track might help. A non-skewed 
system (no skewing of any kind) 
would have the sectors numbered in 
order and the directory sectors 
would correspond with the sector 
numbers. A standard disk would 
have the sector numbers in order but 
the second directory sector would 
not be found in sector number two 
but in sector numl)er seven. A hard 
skewed track would find sector 
number two in the seventh sector 
from the beginning location. The 
standard system will use a skew 
table and the hard skew will not. 
What most people have problems 
with is how the system performs this 
operation. The operating system will 
ask for a logical sector number. The 
BIOS will change (or not) the sector 
number into the skewed value (2 
becomes a 7 in standard systems). 
This value is then stuffed into the 
disk controller sector register and 
used to find the actual sector. You 
must remember that it is you that 
tells the controller which sector to 
get and it reads the ID mark to find 
that sector. A common misunder- 
standing is the use of the index hole. 
Some early systems counted sectors 
starting at the index hole and the 
recorded sector number was unused. 
Most new disk controller chips 
however use the formatted sector ID 
mark to find the proper sector. 

It is my understanding that on 
most new systems you will find the 
index hole used only for full track 
reads and writes. Some chips like the 



NEC 765 also provide their own for- 
mat options. The WD179X series 
uses a full track write for formatting 
(you supply the data string). The 
most common use for the Index 
timing mark is to check disk size 
(five and eight inch timing is dif- 
ferent) and for disk status (ready) 
condition. 

We can conclude this discussion by 
reviewing how to copy or use a dif- 
ferent formatted disk. First is to do a 
full track read through a hand 
assembled program or your 
system's monitor. This wUl give you 
the sector size, skewing information, 
and density (single or double). For 
double sided drives you will need to 
check the track order as some 
systems go from side to side (all odd 
number tracks on one side of the 
disk) while others fill one side before 
going to the other side (the ID mark 
tells which side, hopefully). The next 
operation is to use the listing of your 
BIOS (the PRN fUe) and find the 
disk's DPBA table (can be found by 
using DDT if you know what to look 
for). This table has the address for 
the DPB (parameter blocks which 
tell the system block size, number, 
etc.) and the XLT (translation table 
for skewing). For no skew systems 
the XLT can have all zeros, for 
others it will point to a table of skew 
values. The translation program 
steps through the table based on the 
logical skew number. The value in 
the table is then sent to the disk con- 
troller. Patching \i\e table with DDT 
will work for different skews. 

Many little things must be kept in 
mind however. Your BIOS must 
support double density or larger 
blocks, to be able to read double den- 
sity disks. If the number of sectors or 
blocks is different than before, new 
values will be needed in the DPB. 
Systems can have a different num- 
ber of system tracks and the offset in 
the DPB must match. Side differen- 
ces will need to be checked as 
system programmers do it differen- 
tly.