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OOOSSThe  Boston  Computer  Society 


Volume  2,  Issue  4 

April  1983 

This  newsletter  is  produced  to  inform  group  members  of  the  agenda  and 
logistics  for  future  meetings,  as  well  as  to  recap  and  amplify  the  information 
provided  at  the  last  meeting.  It  also  provides  a  forum  for  members  and 
interested  parties  to  communicate  what  they  have  learned  or  developed  relating 
to  Sinclair  and  Timex  computer  products.  Meetings  are  open  to  the  public; 
however,  attendees  are  encouraged  to  join  the  Boston  Computer  Society  (BCS). 
This  newsletter  is  free  to  members.  Back  issues  are  one  dollar  each. 


Date:  Wednesday,  April  13,  1983 

Time:  7:00  p.m. 

Place:  Large  Science  Auditorium 

UMass,  Harbor  Campus 
(Directions  on  last  page) 

In  April,  Dave  Wood  will  present  his  printer  interface  with  the 
Sinclair-Timex  computer.  The  printer  is  the  Okidata  Microline  92,  a  full- 
width  dot  matrix  printer  which  expects  a  Centronics-type  interface.  He  uses 
the  CAI/0  interface  board  from  CAI  Instruments.  Dave  will  describe  the 
hardware  and  software  required  for  the  interface.  In  addition,  Dave  will 
describe  how  to  get  listings  of  BASIC  programs  with  printers  that  can't 
utilize  the  LLIST  capability  of  the  computer. 

Sue  Mahoney  will  demonstrate  MAtor  the  ABC  Gator,”  a  new  software  package 
from  Timex.  Ator  was  designed  to  teach  ABCs  to  preschoolers.  It  introduces  a 
new  technique  of  combining  the  audio  from  the  tape  recorder  with  the  operation 
of  the  computer. 

Following  the  presentations,  we  plan  to  break  into  special  interest 
groups  to  discuss  topics  of  interest.  Tentatively,  an  advanced  and  a 
beginner's  group  are  planned. 

At  the  May  meeting  which  will  be  held  on  the  third  Wednesday  of  the 
month  (May  18),  Dan  Roy  will  unveil  an  add-on  color  capability  for  the 
TS-1000  he  developed.  The  product  will  be  called  ColorSin  81.  It  provides 
color,  sound,  and  joy  stick  with  no  modification  to  the  Sinclair-Timex 
computer.  Also,  Dan  will  demonstrate  the  CAI  stringy  floppy  mass  storage 
device,  which  he  says  was  essential  for  the  development  of  ColorSin  81. 

If  you  have  items  to  discuss  at  a  future  meeting  or  suggestions  for 
presentations,  contact  Sue  or  Cliff. 


The  first  item  at  the  last  meeting  was  Bob  Masters'  review  of  Henry 
April's  keyboard.  The  keyboard,  sold  by  Henry's  company,  E-Z  Key,  sells  for 
$84.95  plus  shipping  and  handling.  (BCS  members  can  save  shipping  and 
handling  charges  by  ordering  the  keyboard  from  Henry  and  picking  it  up  at  the 
meeting.)  Bob  gave  a  brief  review  of  Henry's  development  process,  one  which 
Henry  shared  with  us  over  the  past  year.  Henry  first  designed  the  keyboard 
features,  and  then  attempted  to  get  a  keyboard  with  a  style  and  feel  which  he 
was  confortable  with.  Bob  likes  the  keyboard  and  the  personalized  service 
Henry  has  afforded  BCS  members.  See  a  review  article  by  Bob  in  the  March 
issue  of  Syntax. 

Next,  Will  Stackman  reviewed  MCODER,  an  integer  compiler  (see  page  3). 

Will  explained  a  compiler  is  a  computer  program  which  translates  programs  into 
machine  language .  The  Sinclair-Timex  BASIC  is  an  interpreter.  Compiled 
programs  run  much  faster  that  interpreted  programs.  Also,  Peter  Nichols  gave 
a  brief  demonstration  of  another  integer  compiler  sold  by  Bob  Berch,  19  Daques 
Street,  Rochester,  New  York  14620.  Both  compilers  appeared  relatively  easy  to 
use.  The  compiled  code  was  impressively  fast.  It  was  stated  that  Non-Trival 
Solutions,  P.0.  Box  2941,  Amarillo,  Texas  79105  also  sells  an  integer  compiler. 

Larry  Becker  gave  a  very  interesting  demonstration  of  an  intelligent 
laboratory  station  terminal  he  has  developed.  Larry  is  on  sabbatical  leave 
from  Hiriam  College  in  Northeast  Ohio.  He  developed  the  system  while  at  the 
Technical  Education  Research  Centers  (TERC)  in  Cambridge.  His  terminal 
consists  of  the  Timex  TS-1000  computer  plus  an  additional  card  of  electronics. 
The  system  allows  up  to  16  TS-1000  terminals  to  interface  with  a  single 
central  Apple  computer.  The  terminal  has  parallel  input/output  and  an 
analog-to-digital  interface.  A  digital-to-analog  interface  is  also  planned. 
Data  can  be  collected  and  displayed  by  the  TS-1000  terminal.  In  addition, 
data  can  be  automatically  relayed  to  the  central  computer.  At  the  central 
computer,  the  data  can  be  stored  on  floppy  disk  or  displayed  on  high- 
resolution  color  monitors.  The  central  computer  allows  student's  data  to  be 
processed,  averaged,  graded,  and  so  on. 

In  Larry's  demonstration,  data  on  the  motion  of  a  pendulum  was  observed. 
He  mounted  a  potentiometer  with  a  pendulum  attached  on  the  side  of  a  table. 
After  setting  parameters  for  voltage  levels  and  sampling  time  (this  was  easy 
with  the  menu  driven  program  he  wrote),  the  rotational  motion  of  the  pendulum 
versus  time  was  sampled.  A  beautiful  low-resolution  graph  of  a  sine  wave  was 
plotted  by  the  TS-1000  computer.  Larry  then  changed  a  few  parameters  and  the 
500  sample  points  were  almost  instantaneously  transferred  to  and  displayed  on 
the  Apple  computer. 

The  board  Larry  designed  to  interface  the  Timex  computer  uses 
approximately  ten  chips.  The  main  chips  are  an  8255  parallel  input/output 
chip,  a  0809  analog-to-digita.1  converter,  and  a  75117  tristate  differential 
serial  buff er/ transceiver .  The  interface  at  the  Apple  was  just  another  75117 
wired  to  the  paddle  port!  Larry  currently  operates  the  interface  at 
20  kilobaud,  over  a  reversible  3-wire  line.  With  multiple  terminals,  a 
polling  protocol  is  envisioned.  Machine  language  programs  in  both  the  Apple 
and  Timex  are  employed  to  operate  the  interface.  Larry  says  the  target  price 
for  the  interface  board  is  50  to  100  dollars.  The  capability  to  download 
programs  may  be  added. 


MCODER  is  an  integer  compiler  program  for  the  Sinclair-Timex  computer. 

It  runs  on  machines  with  the  8  K  ROM  and  at  least  16  K  RAM.  MCODER  is  sold  by 
Personal  Software  Services,  Coventry,  England.  It  is  available  locally  from 
Intercomputer,  Inc.,  179  Newbury  Street,  Boston,  Massachusetts  02116  for 
$18.95  including  shipping. 

The  MCODER  program  occupies  a  little  over  2  K  of  RAM.  As  a  compiler,  it 
takes  a  program  you  write  in  a  modified  BASIC  language  and  converts  it  to  an 
efficient  machine  language  subroutine.  This  machine  language  subroutine  is 
then  used  in  an  ordinary  BASIC  program.  The  machine  language  program  is 
invoked  by  executing  a  USR  call  to  location  18823.  The  2  K  MCODER  program 
must  remain  in  memory,  as  it  contains  subroutines  used  by  the  compiled  program. 

The  MCODER  BASIC,  the  modified  BASIC  in  which  you  must  write  programs  to 
be  compiled,  allows  only  simple  arithmetic  (+,-,*,  and  /  with  no  SQR,  PI,  LN, 
or  trig  functions),  using  only  integer  (whole)  numbers.  Boolean  operators 
(AND,  OR,  NOT)  are  not  available.  Only  26  single  letter  numeric  variables  are 
allowed.  There  is  only  one  array.  And  there  are  no  string  ($)  variables  at 
all.  Input  is  through  the  use  of  CODE  INKEY,  which  decodes  single  keystrokes. 

The  MCODER  program  is  easy  to  use.  However,  programs  tend  to  be  hard  to 
debug  because  of  the  differences  between  the  MCODER  BASIC  and  the  one  we  know. 
For  example,  the  RND  function  returns  an  integer  value  between  zero  and  32767, 
instead  of  a  floating  point  number  between  zero  and  one.  Another  example  is 
that  a  FOR  NEXT  loop  from  1  TO  3000  is  required  to  allow  enough  time  to  get 
your  finger  off  an  input  key.  There  is  an  error  flag,  but  no  error  codes 
which  would  make  debugging  straightforward. 

MCODER  comes  with  ,,migi,,  (that's  smaller  than  "micro,"  which  is  to  say, 
minimal)  documentation,  which  is  by  far  its  weakest  feature.  Commands  are 
explained  alphabetically,  and  some  information  must  be  inferred.  For  example, 
although  not  mentioned,  you  can  recompile  routines.  Each  time  you  do, 
however,  a  new  REM  is  added  which  can't  easily  be  removed.  Also,  the  one 
example  in  the  instructions  is  wrong.  The  screen-filling  PLOT  example  must 
use  63  for  width  and  40  for  height,  not  100  and  50,  and  the  divisor  for  PAUSE 
is  60,  not  50,  as  in  the  United  Kingdom. 

All  in  all,  as  the  cheapest  and  shortest  compiler  available,  MCODER  is  an 
interesting  piece  of  software.  Its  immediate  uses  seem  limited.  The  most 
interesting  feature,  an  elaborate  SCROLL,  might  be  useful  for  a  long  series  of 
complex  results.  But  the  integer  math  makes  formulating  such  results  (for 
example,  statistical  tables)  quite  impractical. 


You  can  discover  some  interesting  (?)  facts  if  you  do  some  PEEKing  into 
the  ROM.  For  example,  zero  appears  more  times  than  any  other  byte  (single 
byte  numbers  must  be  between  0  and  255).  It  occurs  321  times,  with  169  of 
these  occurrences  (over  half)  in  the  part  of  the  ROM  which  contains  the  pixel 
representations  of  characters.  The  next  most  popular  number  is  205  (CD  hex) 
with  304  occurrences.  This  number  corresponds  to  the  CALL  instruction,  the 
machine  language  equivalent  of  G0SUB.  The  number  153  is  the  only  one  which 
does  not  appear  in  the  ROM.  The  number  29  occurs  29  times. 

PROGRAM  by  Jack  Hodgson 

The  program  below  does  nothing  very  useful,  but  watching  it  amuses  the 
hell  out  of  its  author.  The  display  looks  best  when  run  in  fast  mode. 
Once  you've  figured  out  how  it  does  what  it  does  (which  isn't  too  tough), 
enter  other  values  for  A$. 

10  LET  D=0 
20  LET  C=0 

100  LET  A$=" 135 1281 280041 3 51 28130000 12800700 1000128 

190  LET  E=1 
200  FOR  B=1  TO  8 

300  PRINT  AT  D,C+B-1;CHR$  VAL  A$(E  TO  E+2) 

350  LET  E=E+3 
400  NEXT  B 

403  IF  E>94  THEN  GOTO  450 

404  LET  D=D+1 

405  GOTO  200 
450  LET  C=C+5 

460  IF  C>24  THEN  LET  C=0 
500  PAUSE  60 

698  LET  D=0 

699  CLS 

700  GOTO  190 


Last  month  we  featured  an  article  entitled  "Fresh  Squeezed  Computer 
Data."  In  the  article,  two  subroutines  were  given.  The  first  subroutine, 
beginning  at  line  200,  compressed  input  data  1$  into  A$;  the  second,  at  line 
800,  expanded  compressed  data  in  1$  into  A$.  In  this  article,  we  illustrate 
how  these  routines  may  be  used. 

Consider  a  program  to  store  names  and  telephone  numbers.  Let's  allocate 
20  characters  for  each  name  and  10  digits  for  each  telephone  number.  With  30 
bytes  for  each  entry,  only  34  names  and  numbers  could  be  stored  per  1  K  RAM 
storage.  Using  the  data  compression  scheme,  we  could  compress  the  data  into 
20  bytes  per  entry.  This  would  increase  the  number  of  entries  by  50  percent. 
The  only  change  necessary  to  the  program  published  last  month  is  to  line  2 
to  LET  B=20. 

It  is  possible  to  get  even  more  data  compression  by  using  more 
information  about  names  and  telephone  numbers.  We  know  that  names  require 
only  27  different  symbols  (the  alphabet  and  a  blank);  and  telephone  numbers 
only  require  eleven  different  symbols  (the  numbers  0,1,..., 9,  and  a  blank). 
Using  the  formula  -INT  (-N*(LN  M/LN  2)/8),  where  N  is  the  length  of  the  string 
and  M  is  the  length  of  the  alphabet  (LEN  M$) ,  it  is  possible  to  calculate  the 
number  of  bytes  required.  The  20 -character  name  (N=20,  M=27)  requires  12 
bytes  and  the  10  digit  telephone  number  (N=10,  M=ll)  requires  5  bytes,  or  a 
total  of  17  bytes  per  entry.  Thus,  we  get  60  entries  per  1  K  of  storage  or  a 
75  percent  increase  over  the  original  capacity. 


Below  Is  the  code  for  the  data  compression  technique  described  on  the 
last  page.  If  you  start  at  line  5,  the  data  is  compressed  into  the  string  D$. 
Starting  at  line  500  the  Dth  data  entry,  where  D  is  the  input  parameter,  is 
decompressed . 

10  LET  D$=" " 

15  LET  T=256 

30  INPUT  1$ 

32  IF  LEN  I$=0  THEN  GOTO  25 
35  GOSUB  100 
40  GOSUB  200 
45  LET  D$=D$+A$(  TO  B) 


60  INPUT  1$ 

62  IF  LEN  I$=0  THEN  GOTO  55 
65  GOSUB  150 
70  GOSUB  200 
75  LET  D$=D$+A$(  TO  B) 

80  GOTO  25 




125  LET  N=20 

130  GOTO  600 


160  LET  M$="0123456789  " 

175  LET  N=10 
180  GOTO  600 

610  LET  M=LEN  M$ 

620  LET  B=-INT  (-N*(LN  M/LN  2)/8) 

630  DIM  K(B) 

640  RETURN 


510  INPUT  D 

515  LET  I$=D$(D*17-16  TO  D*17-5) 

520  GOSUB  100 
525  GOSUB  800 
530  LET  N$=A$ 

535  LET  I$=D$(D*17-4  TO  D*17) 

540  GOSUB  150 
545  GOSUB  800 
550  LET  P$=A$ 

555  PRINT  N$ ; "  ";P$ 

560  GOTO  505 

The  example  illustrates  how  one  uses  a  data  compression  technique.  Even 
further  data  compression  could  be  achieved  if  variable  length  records  were 
allowed . 


In  February,  Chuck  Durang  on  behalf  of  Reston  Publishing  Company  donated 
five  books  to  the  user  group  library.  They  are: 

Mastering  Machine  Code  on  Your  ZX-81  by  Toni  Baker 

Making  the  Most  of  Your  ZX-81  by  Tim  Hartnell 

49  Explosive  Games  for  the  ZX-81  by  Tim  Hartnell 

The  ZX-81  Pocket  Book  by  Trevor  Toms 

Fifty  1  K  /  2  K  Games  for  the  ZX-81  and  TS-1000  by  Allistair  Gourlay, 
James  Walsh,  and  Paul  Holmes 

In  addition,  we  have  Byteing  Deeper  into  Your  TS-1000  by  Mark  Harrison,  which 
was  donated  by  Tom  Bell  of  Addison-Wesley  Publishing  Company.  To  borrow  these 
books  see  a  member  of  the  library  committee  at  the  next  meeting. 


Updating  the  list  of  books  available  in  the  Boston  area  (see  the  February 
newsletter),  R.  F.  Valle  reports  having  found  the  following: 

Charlton,  Mark.  The  Gateway  Guide  to  the  ZX-81  and  ZX-80,  More  Than  70 
Programs .  Morris  Plains,  New  Jersey:  Creative  Computing  Press,  1981. 

Hartnell,  Tim.  Getting  Acquainted  With  Your  ZX-81  (Third  Edition),  More 
Than  80  Programs.  Morris  Plains,  New  Jersey:  Creative  computing  Press, 

Page,  Edward.  37  Timex  1000  Sinclair  ZX-81  Programs  for  Home,  School, 
Office .  Woodsboro,  Maryland:  ARCsoft  Publishers,  1983. 

Page ,  Edward .  101  Timex  1000/Sinclair  ZX-81  Programming  Tips  and  Tricks. 

Woodsboro,  Maryland:  ARCsoft  Publishers,  1983. 


Sue  Mahoney  informed  the  group  that  the  Timex  printer  is  being  shipped. 
She  also  said  the  Timex'  computer  newsletter  is  being  prepared.  It  will 
be  called  Ramblings. 

TWO  MEMORIES  IN  ONE  SPACE  by  Dave  Wood 

Many  of  the  new  Timex-Sinclair  add-ons  make  use  of  the  unused  address 
space  between  the  ROM  and  RAM  (memory  addresses  8192  through  16383).  However, 
if  you  buy  devices  from  more  than  one  vendor,  this  "unused"  memory  space  can 
soon  become  over-used.  Following  is  a  quick-and-dirty  solution  I  use  to  share 
(or  multiplex)  the  address  space  for  a  CAI/O  interface  which  drives  my  printer 
and  my  home-made  static  memory  (used  to  store  machine  code).  The  only  part 
required  is  a  simple  double  pole  double  pole  (DPDT)  switchand  a  small 
resistor.  The  switch  selects  which  of  the  two  equipments  use  of  the  memory 
space.  Obviously,  both  cannot  be  selected  at  the  same  time. 

The  activation  of  a  device  in  8-to-16  K 
memory  area  depends  upon  the  voltage  states  of 
some  of  the  lines  which  come  out  on  the  back 
edge  connector.  It  is  usually  a  logical  zero 
(zero  volts)  on  one  specific  line.  In  the 
case  of  the  CAI/O  interface,  the  entire 
interface  box  is  activated  by  the  MREQ  line 
(pin  14  on  the  top  edge  connector)  going  to 
logical  zero.  If  this  signal  doesn't  get  to 
the  CAI/O,  the  interface  is  inoperative  — 
that  is,  it's  internal  EPROMs  are  not  used. 

In  the  case  of  my  memory,  the  RAM  chip  select  line  (CS)  goes  to  logical  zero 
when  the  proper  address  is  decoded.  If  the  CS  is  held  at  logical  one  (+5 
volts),  then  my  memory  is  inoperative  (but  it  still  remembers  all  that  is  in 
it).  Above  is  the  wiring  of  the  DPDT  switch.  I  made  the  MREQ  line 
connections  on  an  interface  connector  between  the  computer  and  the  CAI/O. 

Thus,  no  modification  to  the  computer  or  to  the  CAI/O  were  required. 


~l  PT 


^  DPDT  Switch 

5  v  V* /A  •  T  *  From  RAM  Selector 
To  RAM  CS 


In  the  May  issue  of  this  newsletter,  we  plan  to  begin  publishing  paid 
advertising.  We  are  doing  this  for  two  reasons.  First,  there  are  costs 
involved.  The  BCS  has  been  very  supportive,  actually  unquestioning.  But  if 
we  continue  to  grow,  as  we  plan,  we  will  soon  be  more  of  a  burden  than  it  is 
fair  to  expect  the  BCS  to  bear.  The  second  reason  is  that  advertising  will 
give  our  readers  another  forum  for  examining  the  products  and  services  that 
are  available  to  them. 

We  do,  however,  want  to  make  some  important  points.  We  shouldn't  even 
need  to  say  that  editorial  (reviews  ...)  will  be  independent  of  advertisers. 
This  publication  in  no  way  endorses  products  advertised,  nor  disparages  ones 
that  are  not.  In  addition,  only  a  small  portion  of  the  newsletter  will  be 
devoted  to  ads.  Advertising  space  will  be,  within  certain  public  guidelines, 
assigned  on  a  first-come,  first-served  basis.  We  have  given  much  thought 
toward  creating  a  policy  that  will  showcase  advertisers  that  are  of  value  to 
our  readers  and  screen  out  others.  These  policies  will  evolve  over  time.  We 
seriously  solicit  your  comments  on  them  (as  well  as  other  aspects  of  this 
newsletter  and  user  group).  Next  month  we  take  the  plunge.  We  hope  to  use 
this  opportunity  to  better  serve  you.  It  may  take  us  a  couple  of  issues  to 
get  the  hang  of  it.  Your  help  is  welcome  and  your  forbearance  is  begged  and, 
oh  yes,  if  you  want  to  buy  an  ad,  please  call. 


Sue  Mahoney,  Director  of  the  Sinclair-Timex  User  Group 
c/o  The  Boston  Computer  Society  or  call  (203)  573-5816. 

Cliff  Danielson,  Newsletter  Editor 

14  Davis  Road,  Chelmsford,  MA  01824,  (617)  256-4638. 

John  Kemeny,  Contributing  Editor  &  Correspondent  With  Other  User  Groups 
284  Great  Road,  Apt.  D5,  Acton,  MA  01720. 

Library  Committee:  Beth  Elloitt,  Sean  O'Rahilly,  and  Bob  Sanchez. 

Computer  Related  Products  .and  Services  Only 
Open  Rate:  $40  per  Quarter  Page 
For  Complete  Rate  Card  and  Discount  Information  Contact 
Jack  Hodgson,  P.0.  Box  526,  Cambridge,  MA  02238 


The  Sinclair-Timex  User  Group  meets  in  the  Large  Science  Auditorium  (Room 
8/2/009)  of  the  University  of  Massachussets  of  Boston,  Harbor  Campus.  The 
Harbor  Campus  is  only  3  miles  from  downtown  Boston  and  easily  accessible  by 
public  and  private  transportation.  From  the  north  or  west,  take  the  Southeast 
Expressway  to  Exit  17.  Turn  left  onto  Columbia  Road.  Enter  the  rotary  and 
take  the  first  right  (Morrissey  Boulevard).  Bear  right  on  the  traffic  island, 
following  UMass/Boston  sign.  Turn  left  into  the  Campus.  From  the  south,  take 
Morrissey  Boulevard  northward  to  the  campus.  On  the  META,  take  the  Red  Line 
(Ashmont  Train)  to  Columbia  Station.  Transfer  to  the  free  University 
shuttlebus  in  the  T  parking  lot. 

IMPORTANT  NOTICE  !  If  the  mailing  label  on  this  newsletter  is  handwritten, 
then  you  are  not  on  the  mailing  list  of  the  Sinclair-Timex  User  Group.  You 
need  to  either  join  the  BCS  or,  if  you  are  a  BCS  member,  contact  Mary  McCann 
in  the  BCS  office  to  be  added  to  the  Sinclair-Timex  mailing  list. 

OOThe  Boston 
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