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MINI FLEXIBLE DISK DRIVE INSTRUCTION MANUAL 



TEAC FD-55(L) 
MINI FLEXIBLE DISK DRIVE 
INSTRUCTION MANUAL 



P/N 10131159-OCA 



- i - 



TABLE OF CONTENTS 

Title Page 

2-1 INSTRUCTIONS FOR HANDLING 201 

2-1-1 Disk 201 

2-1-2 Disk Handling 205 

2-1-3 Write Protect 209 

2-1-4 FDD Handling , 210 

2-1-5 Installation and Ejection of Disk 211 

2-1-6 Precautions for Transportation 213 

2-2 INSTRUCTIONS FOR INSTALLATION 214 

2-2-1 Precautions for Installation 214 

2-2-2 Connector and Cable Connection 216 

2-2-2-1 Signal connector and cable 217 

2-2-2-2 Power connector an'3 cable ...,...,.., 221 

2-2-2-3 Frame grounding 223 

2-2-3 Setting of Straps and Terminator 225 

2-2-3-1 Terminators and interface drivers 226 

2-2-3-2 Straps , 229 

2-2-3-3 Turn-on conditions of front bezel indicator 237 

2-2-3-4 Rotating conditions of spindle motor 240 

2-2-3-5 Operating conditions of head load solenoid 242 

2-2-4 Inductive Noise in Installed Environment 244 

2-2-5 Front Bezel 248 

2-3 CONTROL PROCEDURE 250 

2-4 POWER SUPPLY 255 

2-4-1 Power On and Off 255 

2-4-2 Internal Current Consumption of the FDD 257 

2-4-3 Current Consumption Timing Chart 261 

2-5 WRITE/READ METHOD 264 

2-5-1 Single Density 265 

2-5-2 Double Density 267 



- xi - 



2-1. INSTRUCTIONS FOR HANDLING 

The TEAC FD-55(L) series mini flexible disk drive (hereinafter referred 
to as FDD) does not require specially delicate handling as long as it is 
handled according to the following instructions. 

The same care as other similar mini flexible disk drives is required. 
Read through and referred to this Instruction Manual before your operation 
or system design so that the FDD can show the expected performance. 

2-1-1. Disk 

Two types are commercially available for 5.25 inch (mini) flexible disks 
(hereinafter referred to as disk) according to the sectoring of a track. 
One is hard sectored method, which detects each sector photo-electrically 
by means of sector holes. The other is soft sectored method which 
records an identification pattern on the initial position of each sector. 
The FD-55 may be used with either type of disks. Generally, hard sectored 
disk is used only for some specific applications. 

Fig. 201 shows the external view of the disks. The only difference is 
that the hard sectored disk has the same number of sector holes as the 
number of sectors, on a concentric circle together with an index hole. 
The disk itself on which data are recorded is made of 80um thick 
polyethylene film with coated magnetic surfaces. The disk is protected 
in a vinyl chloride jacket with liner to retain dust without damage to 
the disk surface. The jacket has open areas; disk positioning and disk 
driving window (central window) , oval window for magnetic head contact 
with the disk (head window) , and index/sector hole detection window 
(index window) . 

In order to maintain high data reliability, it is recommended to use 
high quality disks. 



- 201 - 



133. 3mm 



Jacket 



Central window 



Notch (write enable notch) 



Index window 




Innermost track 



Outermost track 



Sector holes 



Soft sectored disk 



Hard sectored disk 



(16 sectors) 
(Fig. 201) External view of disk 



- 202 - 



There are many types in the commercially available soft sectored disks 
which are classified according to the following factors. Select the most 
appropriate one for your application. 

(1) Data recording density 

Single density (FM method) or Double density (MFM method) 

Do not use a single density disk for a double density recording. 
Expected data reliability will not be obtained and error may occur. 
A double density disk can be used for a single density recording. 
All the models of FD-55A^ F are used for both single and double 
density recordings. 

(2) Number of used sides 

Single sided (only side can be used) or double sided (both sides and 
1 can be used) . 

Use a double sided disk for a double sided FDD. If a single sided disk 
is used for a double sided FDD, data reliability of the side 1 might be 
degraded . 
A double sided disk can be used for a single sided FDD. 

(3) Track density 

48tpi or 96tpi. 

It is recommended to use a disk of the same track density as the track 

density of an FDD. If a 48tpi disk is used for a 96tpi FDD, the data 
reliability might be degraded rarely. 

Though such an application of using a 96tpi disk for a 48tpi FDD does not 

cause practical problem, it is not thoughtful to use in that way. 



203 



(4) Track numbers 

Some of commercially available 48tpi single sided FDDs can access only 

35 tracks from track 00 to 34. And 35 track disks are used by some 

people in a few application. 

The operation of the FD-55A is guaranteed for track 00 through 39 (total 

40 tracks). However, the data reliability of five tracks from 35 to 39 

are not guaranteed when a 35 track disk is used. 

Almost all the disks commercially available are guaranteed for up to 

40 tracks. 

(5) High density disk 

For the high density FDD (FD-55G) which is put to practical use recently, 
use an exclusive HD disk. Do not use disks for FD-55A ^ F. 
Generally, disks written by an FD-55A ^ F cannot be read by an FD-55G. 
Do not use an HD disk with FD-55A ^ F. The data reliability may be 
degraded. 



204 



2-1-2. Disk Handling 

Disk is a precision recording media. Be sure to observe the following 
precautions. 

(1) Do not tear, fold, or distort the jacket or disk. 

(2) Do not install a damaged disk in the FDD, damaged disk not only disturbs 
the normal read or write operation but also it may damage the FDD. 

(3) Do not touch the opening areas of the jacket (magnetic coating area of 
the disk) . Fingerprints left on the disk will cause errors. 

For manual handling of the disk, it is recommended to hold the label 
area in Fig. 202. 



Disk (Jacket) 



Opening areas of jacket 




Label area 

Write enable notch 

Envelope 



(Fig. 202) Protective envelope and label area of the disk 

(4) Return the disk to its envelope for the protection of the window area 
whenever it is removed from the FDD. The disk should not be left 
outside of the protective envelope such as on a desk even for a while. 

(5) For a long term storage, keep the disk in a protective container with 
the envelope in an upright position. 

For a short term storage, a few disks may be piled horizontally without 
a container. Do not lean the disks and do not place any heavy objects 



- 205 - 



such as books on the disk, which will cause distortion of the disk. 

(6) Keep and use the disk away from dust. Also do not install a dusty 
disk into the FDD. Such dust, if carried to the magnetic head, may 
cause data errors and may shorten the life of the disk and the FDD. 

(7) Do not clip the jacket. The clipped portion will be distorted. 

(8) Do not write on the index label of the jacket with a hard tipped object 
such as a lead pencil or a ball point pen which may damage the disk 
surface. Use a soft writing object which will not damage the disk such 
as a felt tip pen. 

Generally, it is desirable not to write on a label which is already 
stuck on the disk. It is recommended to stick the label after writing 
the information. 

(9) DCS not rub out the information on the label with an eraser. Rubbish from 
the eraser may get into the jacket. 

(10) Index label shold be applied on the label area shown in Fig. 202. 
Do not apply more than two labels on the same area. 

m 

(11) Keep the disks away from magnetic fields such as by magnets, transformers, 
motors, etc. These may degrade the recorded data on the disk. The 
ambient stray magnetic field should not exceed 50 Oersted. 

(12) Do not smear the disk with a solvent such as thinner, freon, or alcohol, 
it damages the magnetic coating of the disk. 

(13) Do not expose the disk to sunlight, micro-waves, or infrared ray. Keep 
the disk away from heater or stove. Also do not put the disk on the 
electric apparatus such as TV set. 

(14) Disks should be operated within the following conditions: 

- 206 - 



Ambient temperature: 10°C ^ 51.5°C <50°F 'v 125°F) 

Relative humidity: 20% "\< 80% 

Wet bulb temperature: 29°C (84°F) , Max. 

The above temperature applies to the jacket surface. In the actual 

operating condition, approximately 15 °C of temperature margin is 

required against the operating limit taking the temperature rise in the 

FDD assembled in a host system into consideration. 

Generally upper limit of the temperature is determined by a deformation 

limit of the jacket material because the jacket deformation disturbs 

good contact between the disk and the magnetic head which may degrade 

performance characteristics . 

Also a sudden change in environmental conditions should be avoided even 

within the specified range. 

(15) Disks should be stored within the following conditions: 

Ambient temperature: 4°C ^ 51.5°C (40°F ^ 125°F) 
Relative humidity: 8% "»-■ 80% 

(16) For transportation, disks should be in the protective container. It is 
recommended that a sufficient space exists between the recorded disk and 
outer surface of the final container, so that risk of damage due to 
stray magnetic fields will be negligible. 

Disks should be transported within the following conditions: 

Ambient temperature: -40°C ^ 51.5°C (-40°F ^ 125°F) 
Relative humidity: 8% -v. 90% 
Temperature gradient: 20°C/hour 

(17) Disks which have been stored or transported at temperature and humidity 
exceeding the operating conditions may exhibit degradeed performance. 
Such disks should be subjected to a conditioning period of not less than 



- 207 



24 hours within the operating environment prior to use. 

(18) When you install the disk to the FDD, be careful to handle it slowly. 
Rough installation will accelerates the degration of the disk and it 
may cause incorrect installation. 



- 208 - 



2-1-3. Write Protect 

A write enable notch is located on the right side of the disk. 
For recording new data, use a disk with the notch in the condition 
shown in Fig. 201 (notch open). When a disk with an open notch is 
installed in the FDD, the FDD enables record current to flow into the 
magnetic head in response to a write command. 

To protect the recorded data from accidental erasure due to operational 
errors, cover the notch with a write protect tab as shown in Fig. 203. 
Writing or erasing by an erroneous write command is inhibited as the notch 
cannot be detected. 

Be careful not to apply excessive pressure or not to distort the jacket 
whenever you attach a write protect tab to the notch. The tab should 
not be attached beyond the side line of the jacket. Also the notch 
should be completely covered by the tab. 




Write protect tab 



o- ' 





'Fold to 
back side 



(A) 



(B) 



(Fig. 203) Write protect tab 



- 209 - 



2-1-4. FDD Handling 

The FDD should be handled according to the following instructions. 

(1) Inserting and ejecting procedure of a disk should be performed 
according to item 2-1-5. 

Insert a disk correctly and carefully. 

(2) A sudden change in environmental conditions such as temperature or 
relative humidity should be avoided as far as possible even if it is 
within the specified range. Sufficient hours of storage is required 
at the new operating condition if there was a sudden change in the 
environmental condition. 

(3) Keep and use the FDD away from dust and damp. 

(4) Remove the disk from the FDD when it will not be operated for a long 
time. 

(5) Keep the FDD away from stray magnetic or electromagnetic fields such as 
by transformer, magnet, CRT display, etc. 

If such a part or equipment is not sufficiently shielded, it may cause 
data errors or degrades data reliability. Refer to item 2-2-4. 

(6) Refer to item 2-2 for installation of the FDD. 

(7) Do not touch the variable resistors or screw adjusting parts in the 
FDD except for trained technicians concerning FD-55. 

(8) For transportation, refer to item 2-1-6 not to apply excessive impact 
to the FDD. 



- 210 - 



2-1-5. Installation and Ejection of Disk 



Front lever 



Head window 



LED indicator 




Label 



Front bezel 



Write protect notch 



(Fig. 204) Inserting direction of the disk 
(1) Installation of disk 

(a) Set the front lever to the position shown in Fig. 204. 

(b) Take out a disk from its protective envelope. 

(c) Hold the label side of the disk and insert it into the FDD with the 
head window facing the inner side and with the write enable notch 
located at the LED indicator side. 

If the FDD is installed horizontally (Fig. 204) , the label side goes up, 
while the label side goes left side when the FDD is installed 



- 211 - 



vertically with front lever up. 

(d) Insert the disk fully and straightly into the FDD with enough care. 

(d') For the models with disk eject option, a light depressing force is 

required for the full insertion of the disk from the point lcm,approx. 
before the bottom. 

When it is inserted to the bottom, a click sound can be heard. Be 
sure to insert it fully. 

(e) Take off your fingers from the disk, and close the front lever by 
turning 90° in the clockwise direction. 



Caution 


: Never close 


the 


front 


lever with 


depressing 


the 


disk 


with 


your 






fingers. If 


the 


disk 


is 


clamped 


with 


bent 


condition, 


the 


disk 


may 




be damaged. 

























(2) Ejection of disk 

(a) Turn the front lever 90° in counterclockwise direction to open the 
lever. 

It is recommended to pinch the lever with two fingers not to apply 
excessive impact. 

(b) Hold the rear side of the disk with your fingers lightly and draw out 
from the FDD. 

(b 1 ) For the models with disk eject option, disk pops out from the FDD when 
the lever is open. 

(c) Put the disk back into the protective envelope (See Fig. 202). 



- 212 - 



2-1-6. Precautions for Transportation 

The following precautions should be referred to for transportation 
of the FDD and the system in which the FDD is assembled. 

(1) In order to protect the magnetic head assembly from vibration and impact 
during transportation, be sure to attach the protection sheet to the 
FDD. The protection sheet, which is made of thick paper shaped like 

a disk, is installed to all the FDDs at the shipment from the factory. 

(a) The insertion of the protection sheet is done like a disk installation. 
After closing the front lever, pull up the projection of the sheet 

and fix the lever. 

(b) When ejecting the protection sheet, open the lever depressing the 
projection of the sheet with your finger. Store the removed protection 
sheet for another transportation. 

(2) Be careful not to expose the FDD to excessive moisture. 

(3) Since the FDD is small and light, it might fall or be thrown down during 
transportation. To protect the FDD from such abuse, it is recommended 
to package several FDDs in one box. 

(4) When the FDD is shipped assembled in a system, the system cabinet 
should be enough strong to withstand vibration and impact during 
transportation. Also the packaging of the system should be constructed 
to absorb impact so that the FDD will not suffer from excessive impact. 



213 - 



2-2. INSTRUCTIONS FOR INSTALLATION 

Refer to the following items for installing and assembling of the FDD into 
your system so that the FDD can exhibit the expected performance. 

2-2-1. Precautions for Installation 

(1) Keep the FDD away from dust. 

For example, install the FDD away from the floor, without disturbing 
the operation ability of the FDD. Such care will protect the FDD from 
excessive dust. 

(2) It is recommended to operate the FDD in a well ventilated situation 
Cnatural air cooling should not be obstructed) to dissipate the radiated 
heat. 

When a fan is attached in the system cabinet, install it to draw out 
the air. If the FDD is blown strongly, a large quantity of dust may be 
adhered to the FDD. 

(3) Do not place the FDD near a strong magnetic noise source or a electro- 
magnetic noise source. The magnetic head and read amplifier will pick 
up such noises which may cause errors. Be careful about the installing 
position. See item 2-2-4. 

(4) Do not expose the FDD to sunlight. Keep the FDD away from heater or 
stove. 

(5) Do not place the FDD in an environment with corrosive air. 

(6) Do not place the FDD in a situation subject to strong vibration. 

(7) The screws for installing the FDD should not protrude from the FDD 
surface more than 5mm. 



- 214 - 



(8) Do not apply excessive force when installing the FDD in a system 
cabinet. Frame of the FDD may be distorted which causes misalignment 
of the magnetic head. 

(9) For the connection of the cables, refer to item 2-2-2. 

(10) For the setting of the straps (short bars) and the terminator on the 
FDD PCBA, refer to item 2-2-3. 

The setting to match your system might be different from the setting 
at shipment. Confirm these settings before operation. 

(11) After checking that the head cable of the FDD does not protrude nor that 
it is bent extraordinary, attach the FDD to the system cabinet. 
Protruding cable may be caught by other parts or increases load at head 
seek operation, which cause misalignment of the head or seek errors. 

(12) Fundamentally, the FDD should be installed horizontally with the 
indicator and the front lever up (magnetic head up) , or vertically with 
the left side down and the front lever up. In either orientation, the 
FDD should not form a greater angle than 30° for a 48tpi FDD and 15° 
for a 96tpi FDD against the horizontal plane with the front bezel up. 
Do not install the FDD with the magnetic head down in horizontal 
orientation or the front bezel up in vertical orientation (top loading 
of a disk) . These orientation of the FDD may disturb the stable contact 
between the magnetic head and the disk or may cause misalignment of the 
head. 

As to the other orientations than explained above (such as the orienta- 
tion of the right side down with the indicator up or forming a greater 
angle against the horizontal plane than explained above) , separate 
consideration is required. 



215 - 



2-2-2. Connector and Cable Connection 

The basical electric interface between the FDD and a host system is 

the daisy chaining method through the signal connector (Jl) and the 

power connector (J2) . 

Fig. 205 shows the location of each connector. 

Refer to Fig. 206 as to the cable connection. Also refer to Fig. 101 in 

FD-55 Specification as to the external dimension of the FDD. 

Power connector 

-Signal connector (card edge) 

-Frame ground terminal 

' 66 , 9+2 , | , / 48±1 

14±0.5 




IC socket J3 

Terminator 

Straps 
(Short bars) 



Frame 
grounding 
parts 
(CI, RIO, 
M3 screw) 




(Units :mm) 



(Fig. 205) Interface connector positions 



- 216 



2-2-2-1. Signal connector and cable 



(1) Connector 



A 0.1 inch pitch, 34-pin (17 pins, double row) card edge connector is 
used for the signal connector (Jl) . Refer to Fig. 103 in FD-55 
Specification as to the detailed card edge dimension of the FDD PCBA. 
The even numbered pins of Jl are located on the parts side of the PCBA 
(at the bottom side of the FDD) and are used as the signal terminals. 
The odd numbered pins are located on the dip side of the PCBA and are 
used as the signal ground (0V) lines. (See Table 102 in FD-55 
Specification) . Table 201 shows examples of recommended connectors. 
Select a suitable one, taking the type of the cable used and the handling 
ability into consideration. 



Manufacturers 


3M 


AMP 


Connection method 


Crimping 


Crimping 


Soldering 


Maker 
P/N 


Housing 


3463-0001 


583717-5 


583717-5 


Contactor 


not used 


1-583616-1 


583854-3 


Polarizing key 


3439-0000 


583274-1 


583274-1 


Locking key 


not used 


530213-1 


530213-1 


Crimping tool 


Press: 3440-A 
Locater plate: 
3443-11 
Platen: 3442-3 


90268-1 
(Hand tool) 


not used 


Extraction tool 


unable 


91073-1 


91073-1 


Matched cable 


Flat cable 
3M P/N: 3365/34 
(AWG 28) 


Twisted pair cable 
(AWG 28 ^ 24) 



(Table 201) Cable side matched connectors for signal interface 

- 217 - 



(2) Polarizing key 

A polarizing key slot is fitted between pins No. 4 (3) and No. 6 (5) on 
the PCBA card edge. The polarizing key protects the connector from 
wrong connection (connection of pin No.l to the position of No. 34 and 
No. 2 to the position of No. 33). It is recommended to use a polarizing 
key in the cable side connector. 

As far as the open collector type driver is used for the interface 
driver of the host system side (FDD controller side) , the circuit will 
not be damaged even if the connector is inserted wrongly and power is 
turned on. However, if a disk is installed in this condition, recorded 
data on a track will be erased. 

(3) Locking key 

When you use two locking keys (AMP P/N 530213-1) with AMP P/N 583717-5, 
the two positions for locking key insertion (pin numbers 1 and 2, and 
pin numbers 33 and 34) cannot be used for signal and OV lines. Pin No. 34 
is used for the READY signal. 

For fixing the locking keys, $2 holes above the pins No. 2 and No. 34 in 
Fig. 103 (FD-55 Specification) are used. 

(4) Cable length 

The maximum cable length is easily influenced by disorder or distortion 
of transferred waveform which is caused by mismatching of the impedance. 

For the simple model which has an interface driver at a cable end and 
an interface receiver having a terminator resistor at the another end 
of the cable, considerably long cable can be used. Contrarily, for 
a multiple connection of FDDs such as daisy chaining in Fig. 206, the 
reflection of the output signals from the FDD connected on the halfway 
of the cable is greater since one end of the cable is open condition. 
Therefore, the maximum cable length allowed is shorter than the above 

- 218 - 



explained simple model. In the case of LI < L2, shown in Fig. 206, the 
allowable cable length is remarkably shortened. 
Enough care is required for such a case. 

For the system design, observe the input/output signal waveforms both 
at host and FDD sides carefully assuming the cable connections possible, 
and determine the maximum cable length which enables the interface 
receivers of both sides to receive the signals correctly. The shorter 
the total cable length, the better for the system performance. 
Therefore, it is recommended to select the appropriate length of cable 
for the system construction. 

Though the length is different depending on types of cable and types 
of host side receiver, the maximum cable length in a typical daisy 
chain connection is as follows: 
(Refer to item 2-2-3-1). 

Terminator resistor 330ft : 3m, Max, 
Terminator resistor lKft : 1.5m, Max. 




Signal cable Fundamentally, only the final 

FDD has a resistor network for 
terminator . 

Note:Dmark in the FDD shows the FDD address designated by straps DSO ~ DS3. 

(Fig. 206) Typical connecting scheme for up to 4 FDDs 

- 219 - 



(5) Connecting and disconnecting the connector 

Be sure to turn the power off first. When you plug-in the connector, 
check the orientation of the connector and plug- in straight ly without 
excessive force. If you use a flat cable, never disconnect the connector 
by pulling the cable, since the outermost lines (corresponds to pin Nos. 
1 and 34) of the cable are easily broken by excessive force). 



- 220 - 



2-2-2-2 . Power connector and cable 

(1) Connector 

A nylon housing, 4-pin connector is used as the power connector (J2) . 
Table 202 shows an example of recommended connector for the cable side. 
This connector prevents wrong connection because of the housing 
construction . 

Be sure to turn the power off before connecting or disconnecting the 
connector . 



Manuf ac tur er 


AMP 


Connection method 


Crimping 


Maker 
P/N 


Housing 


1-480424-0 


Contactor 


170148-1 
or 60617-1 


60619-1 


Crimping tool 


90123-2 


90124-2 


Extraction tool 


1-305183-2 


1-305183-2 


Matched cable 


AWG 24 ^ 18 


AWG 20 ^ 14 



(Table 202) Cable side matched connector for power interface 



(2) Cable 



Determine the thickness and the length of the cable so that the voltage 
at J2 connector will be in the specified tolerance range in item 1-4 (1) 
and (2) in FD-55 Specification, taking the voltage drop through the 
cable and the maximum power consumption of the FDD into consideration. 



221 - 



Use the correct contactor and crimping tool to suit the cable thickness 
(see Table 202) . 



- 222 



2-2-2-3. Frame grounding 

As described in item 1-10 of FD-55 Specification, DC 0V is connected 
to the frame of the FDD through CI (O.OluF, 500V) and RIO (100K8) in 
parallel at shipping. Refer to Fig. 109 in FD-55 Specification and 
Fig. 205. CI and R10 are mounted on the PCBA on which interface 
connectors are located, and they are connected to the frame through 
the M3 screw for frame grounding (see Fig. 205). 

DC OV-Frame connection by 0.01\iF// 100KI2 is sufficient for shipping or 
acceptance inspection purpose for FDD unit only (not assembled in the 
system). However, this connection is insufficient for the following 
applications from items (1) to (3) . Secure connection by one of the 
methods in item (A) "\» (C) is required. 

Another frame grounding is required: 

(1) When the FDD is assembled in a system cabinet. 

(2) When the FDD is installed or placed on a metallic plate during tests. 

(For example, installed on the vibration tester, placed on a metallic 
plane in thermostatic oven) 

(3) During electro-static noise test. 
Another frame grounding method: 

(A) Connect the FDD frame securely to the metallic cabinet (system 
cabinet with the installation taps (refer to Fig. 101 in FD-55 
Specification). It is required for the system cabinet to be connected 
to DC OV of the power supply unit by an appropriate method. 

(B) Utilizing the frame ground terminal (faston terminal) at the rear 
side of the FDD, connect the frame ground securely to DC 0V of the 



- 223 - 



power supply unit through a low impedance cable (thicker than 
AWG 14) . 

(C) Connect the test plane or test equipment used for testing the FDD 
to DC OV through a low impedance cable. Otherwise, insert a thick 
insulation plate between the FDD and the test plane (unsuitable for 
vibration tester) . 

If any of the above methods is executed, the frame grounding parts 

(CI, RIO, M3 screw) in the FDD may still be mounted. 

If it is unavoidable to remove these parts for system construction, cut 

off CI and RIO with a cutting plier or replace the M3 screw with a plastic 

one and execute one of either (A) or (B) method. 

If DC OV and the frame are completely open, the FDD is easily suffered 
from electro-magnetic inductive noises and there is no way to discharge 
the static electricity generated by the moving parts in the FDD. And in 
result, expected reliability will not be obtained. 



224 - 



2-2-3. Setting of Straps and Terminator 

The FDD is equipped with 16 straps and a terminator resistor network. 
Users can select an appropriate setting for their systems. 
Be sure to check that the short bars and the terminator are correctly 
set for your system before operation according to this item or items 
1-11 and 1-12 in FD-55 Specification. 

The short bars and the terminator resistor network are mounted on the 
double row pins and IC socket J3 on the bottom side PCBA. 
Refer to Fig. 206 as to the connection of several FDDs by daisy chaining 
(4 FDDs, Max.) 



225 - 



2-2-3-1. Terminators and interface drivers 
(1) FDD side terminator 

Terminators for- the input interface signals are equipped to all the FDDs 
at shipment (refer to item 1-8-1 (3) in FD-55 Specification). 
Terminator resistor for the DRIVE SELECT 0^3 input signals is 
separated from terminators for the other input signals and is soldered 
to the bottom side PCBA of the FDD (refer to Fig. 102 in FD-55 Specificat- 
ion) . All the terminators except for the DRIVE SELECT are packaged as 
a 14-pin resistor network and mounted on the IC socket J3. 



Input signals 

DRIVE SELECT 

DRIVE SELECT 1 
DRIVE SELECT 2 

DRIVE SELECT 3 



Other input signals o 



Straps, 
DSO 



FDD PCBA 



R13 




Fixed terminator (soldered) 
' il 



•to internal circuit 



RAl 



Terminator resistor network (7-circuits) 

r 

■1 — vv»- 



fi3 L J3~ 
Vi4 



-t- 



->+5V 



-».to internal circuit 



(Fig. 207) Terminator connection in FDD 

FD-55 (L) series has two types of termination C3308 type and 1KS2 type) . 

Table 203 shows the details of resistor values and LOW level current for 

each type of termination. 

The feature of 330fl type is a relatively longer cable length and that of 

lKft type is the relatively low current consumption and low noise 

generation. 



226 - 



Items 


FD-55 (L) 


3 3 OJi type 

termination 


1KI2 type 

termination 


Resistor 
value 


DRIVE SELECT (R13) 


330£} 


470fi 


Other input signal (RAl) 


330fi 


1KJJ 


DRIVE SELECT 
line current 
(LOW level) 


Terminator current (il) 


14.8mA 


10.4mA 


Internal circuit current (i2) 


1.6mA 


1.6mA 


Total current (il+i2) 


16.4mA 


12mA 


Other input 
signal current 
(LOW level) 


Terminator current li3 ) 


14.8mA 


4.9mA 


Internal circuit current (i4) 


0.4mA 


0.4mA 


Interface 
driver 


Type 


TTL 7438 


TTL 74LS38 or 
7438 


Sink current capability 


48mA (0.4V) 


12mA (0.4V) 
24mA (0.5V) 



Notes: 1. Resistor values and input signal line current are typical values. 

2. TTL 74LS38 or 7438 are used in an FDD of lKft type termination as 
the interface driver. 



(Table 203) Details of FDD termination types 
(2) Installation and removal of terminators 

For a multiple connection of FDDs in daisy chaining, leave the terminator 

network only on the final FDD as shown in Fig. 206, and remove the 

resistor networks on the other FDDs using a pair of tweezers. 

However, if the interface driver of the host side has sufficient margin 

in sink current capability, resistor networks may be left on multiple 

FDDs. For such a case that an FDD already systemed has resistor 

network and additional FDDs are externally connected in daisy chaining, 

multiple resistor networks are rather favorable. 

Also when the distances between each FDD are rather short, an FDD in the 

halfway may have resistor network instead of the final FDD. 

It is recommended to observe the input/output signal waveforms of the 

host and FDD sides actually for the design of the system. 



227 - 



(3) Host side terminator 

Use the same resistor value as the host side terminator. Or use a smaller 
resistor value within the allowable sink current capability of the FDD 
side driver. 

If the FDD side driver is TTL 7438, 120fl is the minimum, while 430n is 
the minimum for TTL 74LS38. 

(4) FDD side driver 

Refer to table 203 and item (2) . 

(5) Host side driver 

Required current sink capability (IoL) for the host side driver should 
satisfy the following expression Crefer to Fig. 2071. 

For DRIVER SELECT signal line: 

Driver capability > Terminator current (il) + internal circuit current (i2) 

For other input signal lines: 

Driver capability > [Terminator current Ci3) x No. of resistor networks 

mounted] + [Internal circuit current Ci4) x No. of 
FDD connected] 

LOW level output voltage (VoL) of the host side driver shall be less 
than 0.4V. For example, for the FDD with 3308 terminator, such a driver 
as TTL 74LS38 cannot be used since only 12mA is guaranteed for VoL 4 0.4V 
even though it has 24mA capability. Especially, care is required for the 
WRITE DATA and IN USE/HEAD LOAD signals, since these signals are 
received with a Shumitt TTL which LOW level threshold is 0.5V(Min.) 



228 - 



2-2-3-2. Straps 



On the bottom side PCBA of the FDD, 16 straps are mounted. They are 
divided into three pin blocks that are HS ^ MX block, UR ^ RE block, and 
PM block. 



a a 



PM 



HS 


a 


a 


DSO 


a 


a 


DS1 


a 


a 


HM 


a 


a 


DS2 


a 


a 


DS3 


a 


a 


MX 


□ 


□ 



a 


a 


UR 


a 


a 


ML 


a 


D 


IU 


a 


□ 


HL 


a 


a 


SM 


a 


a 


uo 


a 


a 


Ul 


a 


a 


RE 



(Fig. 208) Straps and their locations 

Insertion of a short bar onto the post pin is defined as the on-state 
of the strap. Straps are set to the condition in item "1-11-4 of FD-55 
Specification at shipping. The setting can be easily changed by user 
to the most appropriate condition for the system construction. Reset 
the short bars referring to this item or to items 1-11, 1-12 in 
Specification. Since many combinations are possible for setting the 
short bars, it is desired to reset it by users to avoid the confusion 
at shipping stage. 

(1) Installation and removal of short bars 

Installation and removal of short bars must be done after turning off 
the power . 



229 - 



(a) Installation 

Install a short bar securely to short the two pins Cleft and right 
in parallel) in Fig. 208. There is no restriction for the approach of 
the short bar insertion. However, for the easy visual checking of the 
on-state, it is recommended to insert the metal bar at the upper side 
of the post pins. 

(b) Removal 

To protect from unwanted removal due to vibration and impact, the 
short bars are very securely inserted. If it is not removed when 
nipped up with fingers, pull up slowly with a small round nose pliers. 
Be careful not to damage the parts around it. 

(2) Ordering of short bars 

If more short bars than the standard installation at shipping are required, 
or if short bars as spare parts are required, order with the following 
parts number. 
Short bar TEAC P/N -. 13121149 

Maker P/N : Honda Tsushin Kogyo Co., Ltd. DIC-S252 

(3) HS ^ MX strap block 

(a) MX strap 

The on-state of this strap is used when only one FDD is connected 
to the system. All the input/output signals are valid in this 
condition independent of the DRIVE SELECT signal. 

The off-state of this strap is used when multiple FDDs (4 FDDs, Max.) 
are daisy chained or when input/output signals are enabled by the 
DRIVE SELECT input signal for only one FDD connected. It is necessary 
to set the MX strap off of any daisy chained FDD in a multiple 

- 230 - 



connection. 

This strap has no relation to the turn-^on condition of the front bezel 

indicator and the rotating condition of the spindle motor. 

(b) DSO ^ DS3 straps 

These straps designate the drive number (address) of the FDD in the 

multiple control by daisy cahin connection. 

When the MX strap is off, the same number of the DRIVE SELECT signal 

as an on-state DS strap enables all the input/output signals. 

Any of the four addresses through 3 can be designated. 

The DS strap must be set to different number for each FDD. If multiple 

FDDs are set to a single address, they start operation simultaneously 

for each input signal and cause function errors and data errors. 

Refer to items 2-2-3-3 through 2-2-3-5 for the relation between these 

straps (or the DRIVE SELECT signals) and the operating conditions of 

the front bezel indicator, spindle motor, or head load solenoid. 

(c) HS and HM straps 

These straps determine the head load condition. 

i) For the model with head load solenoid: 

Only when the SM strap in the UR ^ RE strap block is on-state, 

HS and HM straps become effective. 

When the SM and the HS straps are on, the head loading will be 

executed by the DRIVE SELECT signal selected by DSO ^ DS3 straps, 

while the head loading will be executed by the MOTOR ON signal when 

the SM and the HM straps are on. 

Never set both the HS and HM straps on at the same time. The MOTOR 

ON and DRIVE SELECT signals will be wired ORed which disturbs the 

inherent functions of. these two signals. 



- 231 



ii) For the model without head load solenoid (CSS model) : 

HS and HM straps have no meaning for CSS (Contact Start/Stop) models. 
Even though one of these straps is set to on-state, it will have no 
influence to the other functions. However, as a general rule, 
these straps should be set to off-state. 

(4) UR ^ RE strap block 

(a) IU and HL straps 

Straps to select the function of the IN USE/HEAD LOAD input signal 
(signal connector pin number is 4) 

i) For the model with head load solenoid: 

When the IU strap is on-state, the signal of pin number 4 functions 
as the IN USE signal. The IN USE function, independent of the 
DRIVE SELECT signal, is provided to turn, on the front bezel 
indicator and to control the rotation of the spindle motor by setting 
the ML strap in item (d) . Refer to items 2-2-3-3 and 2-2-3-4 for 
the operating conditions of the front bezel indicator and spindle 
motor . 

If HL strap is on-state, the signal of pin number 4 functions as 
the HEAD LOAD signal. If the MX strap is on at this time, the head 
loading will be executed by the HEAD LOAD signal, while the MX strap 
is off, the head loading will- be executed by the ANDed condition 
of the HEAD LOAD signal and the DRIVE SELECT signal selected by 
DSO ^ DS3 straps. 

It is possible to set both of the IU and the HL straps on at the 
same time. In such a case, the signal of pin number 4 has two 
functions of the IN USE and the HEAD LOAD. 

Also both straps may be set to off at the same time. In such a case 
both functions of the signal will be invalid. 

- 232 - 



ii) CSS model: 

For the CSS model without head load solenoid, the HL strap has 

no means. Even though the on-state of the HL strap has no 

influence to the other functions, set it to off-state as a general 

rule. 

Only the IU strap is effective for the CSS models. Refer to 

previous item i) as to its function. 

(b) SM strap 

Strap to enable the HS and HM strap function in the HS ^ MX strap block, 
i) For the model with head load solenoid: 

When used with the HS or the HM strap, head load condition is 
determined. (Refer to item (3)-(c)-i)K 

For the model with head load solenoid, one of the straps HL and 
SM must be on-state. If both of them are off, head loading will 
not be executed. If both of them are on, the function of the HS 
strap becomes ineffective and this combination will not be used. 
Refer to item 2-2-3-5 as to the operating condition of the head 
load solenoid. 

ii) CSS model: 

For the CSS model without head load solenoid, the SM strap has no 
means. Even though the on-state of the SM strap has no influence 
to the other functions, set it to off-state as a general rule. 

(c) UO, Ul, UR straps 

Straps to determine the turn-on condition of the front bezel indicator. 
By the combination of four straps including the IU strap, six turn-on 

- 233 - 



conditions in item 2-2-3-3 can be selected. Any other combinations 
than these six are not used practically. 

Never set both the UO and UR straps on at the same time. The internal 
circuit of the FDD might be damaged partially (READY signal circuit) . 

(d) ML strap 

Strap to select the rotating condition of the spindle motor by an 
external command. 

When this strap is off -state, start/stop of the spindle motor can be 
controlled, as a commercially available conventional FDD, by the 
MOTOR ON input signal. 

When this strap is on-state, the spindle motor will rotate while the 
front bezel indicator turns on in addition to the TRUE state of the 
MOTOR ON signal. 

For example, if "Selection 6" of the indicator turn-on conditions in 
item 2-2-3-3 and the on-state of the ML strap are combined, spindle 
motor of a desired one or desired multiple FDDs among the daisy 
chained (4 FDDs, Max.) can be rotated with a desired timing by the 
IN USE and the DRIVE SELECT signals. Rotating the spindle motor of only 
necessary FDDs improves the life of disks and heads and decreases the 
current consumption. Also shifting the start timing of multiple 
spindle motors respectively (start time: 400msec, Max.J to avoid the 
overlapping of a start (rush) current, peak current capability required 
(current limit value) can be decreased. 

Select the most appropriate spindle motor rotating condition for 
your system referring to item 2-2-3-4. 

(e) RE strap 

This strap is effectively used in a high density FDD (FD-55G(D). 
When this strap is on-state, the head is automatically recalibrated to 
track 00 after power on and the track counter in the FDD is cleared. 
And in the following operation, the FDD memorizes the track position 



234 - 



and switches the low pass filter (.switch filter) of the read amplifier 

between track 43 and track 44. 

The automatic recalibration starts at the initial pre-ready condition 

(refer to item 1-8-1 (13) in FD-55 Specification) after power on 

completes within 255msec (if the head was located on the innermost 

track) . The READY output signal maintains FALSE during automatic 

recalibration . 

The RE strap should be set to on-state for FD-55G(L) . 

Since the switch filter is not used in FD-55A ^ F, the on-state of 

this strap is effective only for the execution of previously mentioned 

automatic recalibration. Though there will be no influence to the 

other functions, set the strap to off-state (automatic recalibration 

is not executed) as a general rule. 

(5) PM strap 

Strap to make the spindle motor rotate automatically at the insertion 

of a disk. 

When this strap is off -state, automatic rotation of the spindle motor 

by the FDD internal circuit will not be executed. 

When this strap is on-state, automatic rotation of the spindle motor by 

the FDD internal circuit will be executed in either of the following two 

conditions . 

(a) When a disk is inserted into the front bezel. 

(b) When the disk is removed. (Note that automatic rotation will not start 
when a write protected disk is removed) 

Automatic rotation will stop in either of the following two conditions. 

(A) When the front lever is closed, disk starts rotation, and the FDD 
becomes the ready state (as far as an external command to rotate the 
spindle motor is not input, the READY signal maintains FALSE). 

(B) lOsec, approx. after the removal of a disk from the FDD. 

- 235 - 



Or in a rare case, when a disk is inserted at the index hole position 
and the front lever is not closed for losec, approx. 

(6) Summary of strap selection 

Table 204 shows the procedure of the strap selection. 



Items 


Related straps 


Items to be 

referred 


With head 

load solenoid 


CSS model 


Front bezel indicator 
turn-on condition 


IU,U0,U1,UR 


IU,U0,U1,UR 


2-2-3-3 


Spindle motor 
rotation condition 


ML,PM 


ML,PM 


2-2-3-3 
2-2-3-4 


Head load solenoid 
operating condition 


HL,SM,HS,HM 


- 


2-2-3-5 


FDD address 
designation 


DSO ^ DS3, MX 


DSO >v DS3, MX 


2-2-3-2 
(3)-(.a),(b) 


Automatic 
recalibration 


RE(G model) 


RE(G model) 


2-2-3-2 
(4)-(e) 



(Table 204) Table of strap selection 



- 236 - 



2-2-3-3. Turn-on conditions of front bezel indicator 

Table 205 shows the turn-on condition of the front bezel indicator. 
Six combinations can be selected by four straps of IU, U0, Ul and UR. 



Selection 
No. 


Strap combination 


Indicator turn-on conditions 


IU 


U0 | Ul 


UR 


1 


- 


- 


- 


" 


DRIVE SELECT 


2 


- 


- 


- 


ON 


DRIVE SELECT x Ready 


3 


ON 


ON 


- 


- 


IN USE 


4 


ON 


ON 


ON 


- 


IN USE latch 


5 


ON 


- 


- 


- 


DRIVE SELECT + IN USE 


6 


ON 


- 


ON 


- 


DRIVE SELECT + IN USE" latch 



Notes: 1. "-" mark indicates the off-state of the strap. 

2. Any other combinations of straps than the above will not 
be used practically. 

3. Never set U0 and UR straps on at the same time. 

(Table 205) Front bezel indicator turn-on conditions 

(1) Selection 1 

When the DRIVE SELECT input signal selected by DSO ^ 3 straps is TRUE, 
the indicator turns on. 

(2) Selection 2 

When the condition of selection 1 is satisfied and also the FDD is in 
ready state, the indicator turns on. Ready state means that a disk 
is inserted, front lever closed, and the disk rotates normally. 
Refer to item 1-8-3 (13) in FD-55 Specification for details. 

(3) Selection 3 



- 237 - 



When the IN USE signal Csignal connector pin No. 4) is TRUE, the indicator 
turns on. 

(4) Selection 4 



When the IN USE flip-flop in the FDD is set, the indicator turns 



on. 



(a) The IN USE flip-flop is set when the DRIVE SELECT signal selected by 
DSO ^ 3 straps becomes TRUE during TRUE-state of the IN USE signal 
(signal connector pin No. 4) 

(b) The IN USE flip-flop is reset when the DRIVE SELECT signal selected 

by DSO ^ 3 straps becomes TRUE during FALSE-state of the IN USE signal. 



IN USE 



DRIVE SELECT 



IN USE flip-flop 






Indicator turns on (Selection 4) 



Indicator turns on (Selection 6) 



500ns .Min. 



500ns ,Min. 



Set 



Reset 



(Fig. 209) IN USE signal latch (Selections 4 and 6). 



(5) Selection 5 



The indicator turns on in either of the conditions of Selections 1 and 3. 



(6) Selection 6 



- 238 - 



The indicator turns on in either of the conditions of Selections 1 and 4. 

Note: The FDDs are set to the condition of Selection 5 at shipping from the 
factory . 



- 239 - 



2-2-3-4. Rotating conditions of spindle motor 

Table 206 shows the rotating condition of the spindle motor. Four basic 
selections are available by the ML and PM straps. 



Selections 


Straps 


Spindle motor rotating conditions 


ML 


PM 


7 


- 


- 


MOTOR ON 


8 


- 


ON 


MOTOR ON + Automatic rotation at disk insertion 


9 


ON 


- 


MOTOR ON + On-state of front bezel indicator 


10 


ON 


ON 


MOTOR ON + Automatic rotation at disk insertion 
+ On-state of front bezel indicator 



(Table 206) Basic selection of spindle motor rotating conditions 

(1) Selection 7 

The spindle motor rotates when the MOTOR ON input signal is TRUE. 

(2) Selection 8 

The spindle motor rotates when the MOTOR ON input signal is TRUE, or 
when a disk is inserted (automatic rotation by the FDD internal circuit) . 
Refer to item 2-2-3-1 (5) "PM strap" as to the details 6f the automatic 
rotation by the internal circuit. 

(3) Selection 9 

The spindle motor rotates when the MOTOR ON input signal is TRUE, or when 
the front bezel indicator turns on (when a turn-on condition in Table 
205 is satisfied) . However, the Selection 2 of the turn-on conditions 
cannot be applied for this purpose. Following shows all the possible 
combinations of the rotating conditions by Selection 9. 



- 240 - 



Selection 9-1: MOTOR ON + DRIVE SELECT 

Selection 9-2: MOTOR ON + IN USE 

Selection 9-3: MOTOR ON + IN USE latch 

Selection 9-4: MOTOR ON + DRIVE SELECT + IN USE 

Selection 9-5: MOTOR ON + DRIVE SELECT + IN USE latch 

Refer to item 2-2-3-3 as to the details of the turn-on conditions of the 
indicator . 

(4) Selection 10 

The spindle motor rotates when any one of the conditions in Selection 9 
(9-1 through 9-5) is satisfied or when a disk is inserted (automatic 
rotation by the FDD internal circuit) . 

Refer to item 2-2-3-1 (5) "PM strap" as to the details of the automatic 
rotation by the internal circuit. 

Notes: 1. The FDDs are set to the condition of Selection 8 at shipping from 
the factory . 
2. Elongation in life and saving in power consumption can be done by 
utilizing the Selection 9 or Selection 10 (refer to item 2-2-3-2 
(4) -(d) "ML strap"). Select the most appropriate rotating 
condition for your application. 



- 241 - 



2-2-3-5. Operating conditions of head load solenoid 

This item applies only for the models with the head load solenoid and 
not applies to the CSS models (without head load solenoid) . 
Table 207 shows the operating condition of the head load solenoid. 
Three head load conditions can be selected by four straps of HL, SM, 
HS, and HM. 



Selection 


Strap combinations 


Head load conditions 


No. 


HL 


SM 


HS 


HM 


1 


- 


ON 


- 


ON Ready + pre-ready 


2 


- 


ON 


ON 


- 


DRIVE SELECT x CReady + Pre-ready) 


3 


ON 


- 


- 


- 


(DRIVE SELECT + MX) x (Ready + Pre-ready) 

x HEAD LOAD 



Notes: 1. "-" mark indicates the off -state of the strap. 

2. Any other strap combinations than the above will not be used 
practically . 

3. Never set HS and HM straps on at the same time. 

(Table 207) Head load conditions 

(1) Selection 11 

When the FDD is in ready or pre-ready state by an external rotation 
command of the spindle motor (MOTOR ON signal or front bezel indicator 
turn-on command) , the head loading will be executed. 

Ready state (or pre-ready state) means that a disk is inserted, front 
lever closed, and the disk rotates normally. 

(2) Selection 12 

When the condition of Selection 11 is satisfied and when the DRIVE SELECT 
signal selected by DSO "v- 3. straps is TRUE, the head loading is executed. 



- 242 - 



(3) Selection 13 

When the condition in Selection 11 is satisfied, and when the MX strap 
is on or the DRIVE SELECT signal selected by DSO *• 3 straps is TRUE, and 
when the HEAD LOAD signal (signal connector pin No. 41 is TRUE, the head 
loading is executed. 

Notes: 1. The FDDs are set to the condition of Selection 12 at shipping 
from the factory. 
2. The condition of Selection 11 is similar to the CSS model which 
has no head load solenoid. It is rather better to use the CSS 
model for this purpose because of fewer parts, shorter access 
time, and no head load impact. 

The time required before enabling the read/write operations is 
635msec for the Selection 11 and 400msec for the CSS model. 



243 - 



2-2-4. Inductive Noise in Installed Environment 

Since the FDD handles minute signals in data reproducing, sufficient 
consideration is required to reduce inductive noise and switching noise. 
Equipment installed around the FDD such as a CRT display, TV set, or 
switching regulator, parts such as transformers, or motors and in some 
cases cables may have a harmful effect on the FDD. This appears as 
noise on the read output from a disk and deterioration in symmetry of 
the read waveform or in peak shifts decreasing window margin of the data 
separator . 

A single FDD or combined FDDs are protected in all conditions from 
inductive or magnetic noise generated by internal parts of the FDD such 
as motors, solenoid, and PCBA by shielding these parts and by shielding 
the magnetic head. Even though these shielding is also effective against 
the external noise, it is not perfect for relatively large noise sources 
such as a CRT flyback transformer, switching regulator, etc. In some 
cases, additional shielding against external noise sources, shielding 
by system cabinet, or consideration for the installation position may 
be required. The following shows examples to observe the influence of 
a noisy environment on the FDD. 

Refer to the examples for your improvement of environmental conditions. 
Especially, it is required to confirm the noise influence at the time 
of system design if the FDD is installed near a CRT display or a switching 
regulator, or if the system in which the FDD is assembled is placed near 
a CRT display. 

Observing method A for influence by external noise sources 

(1) Lengthen the interface cable of the FDD to make apart from the noise 
sources . 

(2) Install a disk and write IF data (125KH2 of WRITE DATA for FD-55A ^ F, 
and 250KH2 for FD-55G) on all over the innermost track. 

- 244 - 



(3}_ Observe the READ DATA output signal in read operation with an 
oscilloscope. For this observation, set the time scale of the 
oscilloscope so that two pulses can be observed and then reduce the time 
scale by variable knob so that three pulses can be observed. In this 
adjustment, find the variable knob position at which the next pulse 
jitter width to the triggering pulse can be observed most clearly to 
measure the jitter width. 



READ DATA ~| [" 



-Jitter width (3) 



READ DATA ~J T 

(Larger external noiserT 



-Jitter width (5) 



Trigger 
(Fig. 210) Influence to the READ DATA waveform by external noises 

(4) Shorten the interface cable length as it was and install the FDD in the 
specified position in the system. 

(5) As in item (2), write new IF data and measure the jitter width with the 
same time scale as in item (3) . 

(6) If the jitter width increases when compared with item (3), the increased 
jitter indicates the influence of external noises. 

It is recommended to arrange not to increase the jitter width as much 
as possible. 

Notes: 1. For a double sided FDD, both sides and 1 should be tested. 

2. By this method, it is rather difficult to judge how much jitter 
width is allowable or to know the noise influence correctly in 
figures. However, this is an easy method to know the noise 
influence without breaking down the system, provided that two FDDs 
are used. 

- 245 - 



Observing method B for influence by external noise sources 

(1) Install the FDD in the system properly. 

Connect leading wires (shielded wires are recommended) from TP9, TP10, 
and TPG of the bottom side PCBA to the two channels of an oscilloscope. 
Refer to item 3-3 of FD-55 Maintenance Manual for the detailed position 
of the test points. 

(2) Set one of the two channels of the oscilloscope to Invert mode and ADD 
them to be able to observe them as one waveform. 

Connect the oscilloscope ground to TPG. Also set both channels to AC 
mode. 

(3) Install a disk and set the head to the innermost track. 

(4) Write 2F data (250KHZ of WRITE DATA for FD-55A ~ F, 500KHz for FD-55G) 
on all over the track. 

If it is difficult to write 2F data, a disk initialization (formatting 
of the track) may be done by a command from host system. 

(5) Measure the read output level (p-p value) after the above writing. 

For the initialized disk, measure the .read level of higher output portion 
on the innermost track (corresponds to 2F) . 

(6) Remove the disk and measure the noise level (p-p value) . 

(7) Calculate the S/N ratio according to the following expression. 



Noise level in item (6) mnfti 
2F read level in item (5) X l ' 



(8) If the value calculated by the above expression is less than 5% (S/N: 
26dB) , the FDD is protected against the external noises. If the value 
is between 5% and 10% (S/N: 20 ^ 26dB) , there will be no problem in 

- 246 - 



practical operation. However, as much improvement as possible is 
recommended . 

If the value is more than 10% (S/N: 20dB or less) , some improvement in 
shielding or reducing noises shall be required since desired reliability 
will not be obtained. 

Notes: 1. For a double sided FDD, both sides and 1 should be tested. 

2. For a 96tpi FDD, the read output voltage is approximately half as 
that of a 48tpi FDD. Also taking a off -track between a recorded 
disk and head positioning of an FDD into consideration, it is 
required to pay enough care for the S/N ratio of a 96tpi FDD. 

It is recommended to design your system with the target of less 
than 5% C26dB) 

3. Recommended S/N ratio in item (.8) is applied only when PLO circuit 
in data separator operates correctly and sufficiently. If a poor 
PLO circuit is used in the host system side, the above S/N ratio 
becomes insufficient. 



- 247 - 



2-2-5. Front Bezel 



Fig. 211 shows the detailed dimension of the standard dront bezel 
(front view) . 

Notes : 

1. When the customer of the FDD designs the front bezel, detailed 
drawings (including the drawing of back side! are required. Ask 
for these drawings when required. 

2. The standard color of the front bezel is black. "PPHOX (Xyron)" or 
"ABS" is used as the material. It is recommended to approve the 
use of these material for an optional order of color. 

3. Fig. 211 does not apply for the models with 1/1 size (twice in height 
than the standard slim line) front bezel. The standard color of 
this model is black and the material is "PPHOX CXyron) " 



- 248 - 



146±0.5 



1+ 

o 









in 
ft 



a, 

n 
a 

t-h 



rt 

cr 
ft) 

N 

ro 



g 

3 
W 
H- 


to 



1+ 



149±0.5 



oo 
i+ 

o 




2-3. CONTROL PROCEDURE 

The following controls are required for the FDD to write and read data on 
a desired track. Read the explanation for the input/output signals in 
item 1-8-3 of FD-55 Specification when you design the system for the 
correct control of the FDD. 

(1) Recalibration to track 00 

At the initial power on, the host system does not know which track the 
magnetic head is positioned on. It is necessary, therefore, to step 
out the head until the TRACK 00 output signal becomes TRUE (recalibratic 
The maximum track seeking distance (when the head carriage is in 
contact with the innermost stopper) for this step-out operation will 
be within the following range. 

48tpi FDD: 48 tracks, Max. 
96tpi FDD: 96 tracks, Max. 

Even if the TRACK 00 signal is TRUE before recalibration, it is ideal 
to execute step-in operations first for 4 through 8 tracks and then 
execute the above recalibration. 

The TRACK 00 output signal becomes valid 5.8msec for 48tpi and 2.8msec 
for 96tpi after the trailing edge of the STEP pulse. Be sure to check 
for the TRACK 00 immediately before the input of the next STEP pulse. 

Note: If the RE strap is on-state (FD-55G) , automatic recalibration (refer 
to item 2-2-3-2 (4)-(e)) is executed by the FDD internal circuit at 
the first pre-ready condition (refer to item 1-8-1 (13)) in 
Specification) after power on, and the input of the first recalibrat 
command is not necessary. 

(2) Starting of spindle motor 



- 250 - 



Start the spindle motor by the MOTOR ON input signal or by a front bezel 
turn-on command (when the ML strap is on-state) . Refer to item 2-2-3-4. 
Installed disk speed is settled to the stable rotation within 400msec 
after the above motor start command, and data read or write operation 
can be done from, this timing for the CSS model without head load solenoid. 
The READY output signal becomes TRUE within 800msec after the start of 
the disk (or motor) 

For a CSS model, control the FDD to rotate the disk by the external 
spindle motor start command only for data read, data write, and head 
seek operations since the head is always in loaded condition which is 
effective for the life of disk and head. However, since the start time 
of the spindle motor is longer than the actuating time of the head load 
solenoid, it will be more convenient to use a method (program) to stop 
the motor rotation when the access to the FDD paused for more than a 
certain period (e.g. 3 through lOsec) . 

For a model with head load solenoid, it is recommended to stop the motor 
when the access to the FDD paused for more than a certain time. This 
is because that the side head usually be in contact with the disk with 
a slight pressure even though in head unloading condition. 

Disk life is specified more than 3xl0 5 passes/track with head loading 
and motor rotating conditions. This corresponds to 167 hrs., approx. 
of continuous operation on one track. 

(3) Head loading 

For a CSS model, the FDD is in head load condition as far as a disk is 
inserted and the front lever is closed. Therefore, the data read or 
write operation can be always executed from 400msec after the start of 
the spindle motor. 

For a model with head load solenoid, data read or write operation can 

be executed from 35msec after satisfying the head load conditions 

""" . . .. ■ »■■" ■«. 

- 251 - 



(refer to item 2-2-3-5) . In order to execute the head loading, it is 
necessary that the disk rotates at a specified speed. The head loading 
will not be executed even if the head load command is input when the 
spindle motor stops . 

If the FDD is used with the SM and HM straps on, the pre-ready state is 
detected 600msec, Max. after the start of the spindle motor and the head 
load operation completes after 35msec (635msec is required in total) . 
The operation executed by this strap combination is almost the same as 
the CSS model operation. Therefore, it is recommended to use the CSS 
models for this purpose only. 

For the head load operation by the other strap combinations than the 
above, pay enough care so that the impact by head loading (tapping impact) 
does rot concentrate at a point on a track (e.g. do not synchronize the 
operation with index pulse)-. 

(4) Head seek 

With a combination of the STEP and the DIRECTION SELECT signals, the 
head will be moved to the desired track. For successive movement in 
the same direction, the STEP pulses should be input with a space of more 
than 6msec for 48tpi FDDs and 3msec for 96tpi FDDs, while the STEP pulses 
should be input with a space of more than 21msec for 48tpi and 18msec for 
96tpi FDDs for a change of step direction (settling time is added) 
The access motion and settling will be completed 21msec for 48tpi FDDs 
and 18msec for 96tpi FDDs after the trailing edge of the last STEP pulse 
and data write or read operation can be performed. 
During these periods, keep the WRITE GATE signal FALSE. 

After the WRITE GATE signal becomes FALSE, do not make the DRIVE SELECT 
signal FALSE nor input the STEP pulse at least for 1msec for FD-55A <v F 
and 590ysec for FD-55G. 

If a desired sector cannot, be found even by 4 through 8 retries after 
the head seek operation, a seek error might have occurred. Execute the 

- 252 - 



same recalibrate operation as after power-on in order to try to set to 
the desired track again. If a desired sector cannot be found still 
after several times of this series of operation, regard it as a hard 
error f unrecoverable error). . 

If error occurs in read operation of data field, execute retry including 
the recalibrate operation as well as the above. 

In read operation when the disk and the drive operate normally, it is 
specified that the recoverable error (soft error) may occur less than 
one per 1Q9 bits . This error rate corresponds to one error per 24 hrs . , 
approx. in continuous randum seek operation. 

For the head seek operation, a method to unload the head before the 

seek is often adopted. However, taking the disk damage caused by 

repetitious impacts of head loading (tapping impact) , access speed, 

and tapping noise into consideration, it is desirable to perform the 

seek operation with head load condition. 

Tapping damage is negregible for a single sided FDD. 

For a double sided FDD, it is specified that no error occurs by 3x10** 

taps to a single point on a track. In practical operation, tappings 

do not concentrate on a specific position, and lxlO 5 taps are allowable 

on a track if they are distributed evenly on the track. 

(_4)_ Side selection 

For a double sided FDD, it is required to designate a desired disk side 
by the SIDE ONE SELECT signal. Do not change the level of the SIDE ONE 
SELECT signal at least 1msec for FD-55A a. F and 590ysec for FD-55G after 
the change of the WRITE GATE signal to FALSE (completion of write opera- 
tion) . The signal may be changed at any time except for the above 
period. 

Do not make the WRITE GATE signal TRUE at least lOOysec after the change 
of the SIDE ONE SELECT signal. 



253 - 



MOTOR ON 
DRIVE SELECT 



TRACK 00 
WRITE PROTECT 



Valid INDEX 
Disk rotation 

READY 

DIRECTION SELECT 
STEP 



-ff- 



0.5ys,Min. 



0.8ys,Min.- 



SIDE ONE SELECT 
(Double sided) 



WRITE GATE 



WRITE DATA 



READ DATA 



. 5y s , Max . 



After 
-400ms 



rF 



-400ms, Max. 



800ms, Max. 
— 0.8ys,Min. 



-1ms, Min. (A^F 
590us 



in. (A^F) 
,Min. (G) 



U~U 



21ms, Min. (48tpi). 
18ms, Min. (96tpi) 



8ys,Max. (A^F) 
4ys,Max. (G) 



4— 0.8ys,Min. 



V 



-Track 00 



Valid after 

-5.8ms(48tpi) 

2.8ms(96tpi) 



lms, Min. (A\,F) 
590ys,Min. (G) 



t < 



2 lms, Min. (48tpi) 
"18ms, Min. (96tpi) 



6ms, Min. (48tpi) 
3ms, Min. (96tpi) 



-ff- 



lms, Min. (A^F) 



590us,Min. (G) 



100Us,Min. 
9 



HFP--I 

lOOys 



lOOys 



8ys,Max. (A\,F) 
4us,Max. (G) 



l-ms(A^F) 
"590Us(G) 




21ms , Min. <48tpi) Val ' id (shaded area) 
18ms, Mm. (96tpi) 



Notes : 

1. READ DATA pulse may be output when the conditions such as the DRIVE SELECT 
are satisfied, even if a disk is not installed. 

2. For a single sided FDD, the timings concerning the SIDE ONE SELECT signal 
will be eliminated. 

3. 



FDD model 


* timina 


** timinq 


With head load solenoid 


635ms, Min. 


35ms , Min. (head loading by DRIVE SELECT) 


CSS model 


400ms, Min. 


0.8ys,Min. 



(Fig. 212) Composite control timing 
- 254 - 



2-4. POWER SUPPLY 



2-4-1. Power On and Off 



There is no restriction for power on or off sequence of +12V and +5V. 

The WRITE GATE input signal shall be kept FALSE state during unstable 

DC power condition, if the FDD power is turned on or off simultaneously 

with the host system or if only the power of the host system side is 

cut off. 

There will be no function errors such as unintended erasing of the data 

or unexpected writing of noise caused by the internal circuits of the 

FDD by any power on or off. 

Generally it is recommended to turn the power on or off after removing 

the disk from the FDD in order to avoid accidents. 



+5V power voltage 3.4V- 



FDD input signal 



Period 1 
Period 2 



FDD output signal 



V//////////W///m 



Normal ODeration area 



W/////////WM0X 



3.4V 



-Period 1 



— Period 2 



Notes: 1. In period 1, the low voltage sensor in the FDD inhibits the 
erroneous recording or erasing even if a wrong input signal 
is received. 

2. In period 2, take care not to make the WRITE GATE signal TRUE 
since the FDD mostly functions for each input signal. 



(Fig. 213) Power on and off timing chart 

The following capacitors are attached to the power line of the FDD PCBAs. 
If you want to know the surge current at power on , put them at the end 



- 255 - 



of power cable for testing purposes. 

+5V power line: 130yF, Max. 
+12V power line: 160yF» Max. 



- 256 - 



2-4-2. Internal Current Consumption of the FDD 

Table 208 shows the detailed current consumption of +12V and +5V power 
for each use in the FDD. 



Use 






+12V (mA) 


+5V (mA) 




Operating condition 


Typical 


Maximum 


Typical 


Maximum 


Spindle motor 
Ass'y 


Rotation stops 


25 


40 


25 


30 




Rotating , 

disk not installed 


45 


70 


+ 


+ 


Rotating, disk installed, 
head unloaded (Note 4,12) 


130 


350 


+ 


+ 


Rotating, disk installed, 
head loaded (Notes 4,5) 


180 


410 


+ 


+ 


Peak at rotation start 
(Note 6) 


700 


800 


+ 


+ 


Average at rotation start 
(Note 6) 


620 


750 


+ 


t 


Forced stop (Note 7) 


620 


800 


+ 


t 


Stepping motor 
Ass'y 


Seek operation I 145 

(Note 8) f 


180 


- 


- 


Seek stops j 

(Note 8) j 


- 


50 


65 


Head load 
solenoid 
(Note 12) 


Energization start 
(Note 9) 


200 


250 


- 


- 


After starting 
(Note 9) 




- 


85 


105 


PCBA circuit 


Waiting 
(Note 10) 


15 


30 


150 


205 


Read operation 


30 


40 


220 


300 






Write operation 


125 


155 


220 


300 



(Table 208) Detailed current consumption for each use 



Notes for table 208: 



- 257 - 



(1) The symbol "-" indicates that the power is not used for that item. 

(2) "Typical" current means the practical value of the average current 
consumption measured with a typical FDD in room temperature and with 
nominal voltage. 

(3) "Maximum" current means that the average value of the current consumption 
does not exceed the "Maximum" value in any normal operations. 
"Maximum" in the item of "Peak at rotation start" means the upper limit 
of the peak value. 

(4) "Typical" current of the spindle motor Ass'y at "Rotating, disk installed" 
shows when a commercially available disk of typical running torque 
(150g.cm, approx. with the spindle axis load ) is used. 

Also "Maximum" current of the spindle motor Ass'y shows when a disk of 
the maximum running torque OOOg.cm, approx.) specified in the 130mm 
flexible disk standards such as ISO, ANSI, ECMA, or JIS. 

(5) "Rotating, disk installed, head loaded" includes data write or data 
read operations. 

(6) Fig. 214 shows a typical waveform of the spindle motor current at 
rotation start . 



Peak at rotation start 

-Average at rotation start 




Ripple current 



Average at 
normal rotation 



400ms, Max. 
Motor on 



Time 
Norma 1 rotation 



(Fig. 214) A typical waveform of spindle motor start current 

- 258 - 



The lasting time of the start current is 400msec, Max. (The same as the 
upper limit of the start time) . And the ripple current is specified 
as within 85% of the absolute value of the average current. 

(7) "Forced stop" means that the rotation of the spindle motor is stopped 
compulsively after the rotation start. Motor servo circuit will 

not be broken by the continuous restriction. 

(8) To the stepping motor for executing the head seek, +12V full power is 
applied only at head positioning time (during track access period 
including settling time) in order to decrease the temperature rise. 
During other operation than positioning, — for example, during waiting 
period, during data write or read after the stop on a desired track, 
+5V is applied. 

Fig. 21 shows a typical waveform of the stepping motor current. 



+12V current 



■Peak at seek (350mA, Max.) 

Average at seek 



+5V current 




Seek starts 

The last step command 

Seek operation 



(+12V applied) 



•75ms,Nom. 
100ms, Max. 



Seek stops 



(+5V applied) 



(Fig. 215) A typical waveform of stepping motor current 

(9) To the head load solenoid, +12V full power is applied only when the 
operation starts in order to decrease the temperature rise . During 
nominal condition after the energization start (during head load 



- 259 - 



condition) , +5V is applied. Fig. 2 16 shows a typical waveform of the head 
load solenoid current. 

At start of the head loading, it is required in order to assure the 
head position against the shock of the solenoid motion that +12V is 
applied to the stepping motor as well as item (_8) . 



Peak at start ( 300mA, Max. ) 
Average at start 



+12 V current 



+5V current 



Peak at start (245mA, Max. 




Average after 
start 



Head unload 



Head load starts 



(Fig. 216) A typical waveform of head load solenoid current 

(.10) "Waiting" means that all the input interface signals are FALSE (HIGH 
level) . 

(11) "Write operation" means the period when the WRITS GATE input signal is 
TRUE. 

(.12) For a CSS model, the item of "Head load solenoid" is not applied. 

As far as the disk is installed, head load condition continues and the 
spindle motor current during head unload is not applied. 



- 260 - 



2-4-3. Current Consumption Timing Chart 

Fig. 217 shows the timing chart of the typical average current consumption. 
Fig. 218 shows the timing chart of the maximum average current consumption. 



- 261 - 



3 5ms, Max. 



4 00ms, Max. 



+12V 



40 



+5V 



225 



620 



100ms, Max. 



* 600ms, Max. 



400ms, Max. 



530 



niii iiiii' 

gQ TTTTnTnT 



r™j-h- mm 



230 



355 



355 



210 



fe 



330 380 
N-J 



'245 



"Y" 
295 



3 



33CT 



100ms, Max. 



210 
SBS 



305 
I 



210 ,„ 



M TTTTT 
ttnr 



380 



230 



225 



620 



530 



1551 

m 



275 



355 




210 



330 380 



295 



Motor 



Power on 
surge 



start 



Disk 
insertion 



Motor on 



Seek 



Motor 



Motor 

off 



start 



Seek 
start 



Head 
unload 



Head load 



Head load 



Write 



Motor on 
Head load command 



Notes: 1. The figures show the typical average current (mA) at each 
operation. 

Average current fflffl X Ri ppie current caused by spindle 

motor 

2. Typical average current means practical value of average current 
consumption measured with a typical FDD in room temperature and 
with nominal voltage. Rotation torque is supposed to be a 
typical one obtained by a commercially available disk. 

3. *: Head loading is executed after the FDD becomes pre-ready 
condition (refer to item 1-8-3 of FD-55 Specification) . 

4. Dotted line shows the case of CSS model. 



(Fig. 217) Typical average current timing chart 



262 - 



400ms, Max. 



+12v Uo_ 
o — I 



790 



30ms, Max. 



100ms, Max. 



400ms, Max. 



^ Peak 
900,Max>^850 



390 



110 

fflfflE 



25H5E 



630 



630 



Has 



450 

msm 



8b 



45gF 450 

HEn nttitnt:; 



1 00ms, Max. 



TTTTTflTT T 

■1 



565 



MM Mi 



.390^ 



*600ms,Max. 



790 



850 



390 

ffiffl 



630 

H 



450 
-ffift- 



\ 300 



+5V 



435 500 



315! 



43! 



500 



500 



'"t 



350 



400 i" 



350 



315 



300 



435 pH 

^7- 



Motor 



Power on 
surge 



start 



Seek 



Motor 



Disk 
insertion 



Motor 

off 



start 



Seek 
start 



Head 
unload 



Head load 



Motor on 



Head load 



Write 



Motor on 

Head load command 



Notes: 1. The figures show the maximum average current (mA) at each 
operation . 

2. The actual average value of current consumption does not exceed 
the "maximum average" •under any operating conditions except for 
some abnormal conditions such as installing a disk of out of 
specification, or forced stop of the spindle motor. 

3. Refer to Notes 1, 3, and 4 in Fig. 217. 



(Fig. 218) Maximum average current timing chart 



- 263 - 



2-5. WRITE/READ METHOD 

The FDD has been designed for excellent stability and easily handled 
recording in both FM (single density) and MFM (double density) modes. 
Improved electrical and mechanical characteristics together with the data 
compatibility with ISO, ECMA, ANSI, and JIS standards for 130mm (5.25 inches) 
flexible disk, assures a better error margin. 

Improvements cover many areas, including disk rotational speed accuracy 
(LSV, ISV) , head magnetic characteristics, head-disk contact, improved 
track positioning, optimized write/read circuitry, improved shielding 
against inductive noise, elimination of spindle motor noise, reduction in 
bit shifts, improved signal-to-noise ratio and so on. Careful consider- 
ation of the FDD controller parameters, such as the data separator window 
positioning, PLO (or VFO) response speed, optimum write pre-compensation 
and environmental considerations such as inductive noise, power line noise, 
dust, temperature, humidity, vibration and so on also contribute greatly 
to the reliability of the system as a whole. 



264 - 



2-5-1. Single Density 

FM method is generally used for single density recording. 

The FDD has been designed to use the FM method for single density 

recording . 

The FM method utilizes two frequency components (IF and 2F) and the 
data density to flux transition density ratio is 0.5, giving a 
redundancy ratio of 0.5, without taking into consideration the necessity 
of gaps, and ID field (track formatting). Data transfer rate is 125KHz 
for FD-55A % F and 50KHz for FD-55G. 

Summary of FM method" 

(1) Data bit (D) is located in the center of the bit cell. 

(2) Clock bit (C) is located at the leading edge of the bit cell. 



Bit cells 



CDCDCDC CDC 



FDD WRITE/READ 
DATA 



Data window 




(50% of data cycle) 



Note: The above timings (us) are for FD-55A ^ F. Timings for FD-55G are 
a half of the indicated values. 

(Fig. 219) Bit correspondance and data window in FM method 

A PLO circuit is not necessary when only the FM method is adopted with 
the FDD and a fixed window can be adopted. The most appropriate window 



- 265 - 



is 6Us for tl and 4Us for t2 in the figure above. The t2 width may be 
wider provided that it is widened in the trigger pulse direction of the 
window (towards the left in the figure above) - 



- 266 - 



2-5-2. Double Density 

MFM method is generally used for double density recording. The FDD has 
been designed to use the MFM method for double density recording. 
M 2 FM method and GCR method do not match the standard model of the FDD. 

By eliminating the redundancy of the FM method, the MFM method enables 
the data density to be doubled without increasing the flux transition 
density on the disk. FDD controller will necessarily be more compricated 
with the addition of PLO circuit, but this is compensated for by the 
great increased in the recording capacity. 

The MFM method has three frequency components, IF, 4/3F and 2F. The 
data density to flux transition density ratio is 1 (redundancy :0) 
without taking into consideration the necessity of gaps and ID field 
(track formatting) . Data transfer rate is 250KHz for FD-55A ^ F and 
500KHZ for FD-55G. 

Summary of MFM method: 

(1) Data bit (D) is located at the center of the bit cell. 

(2) Clock bit (C) is located at the leading edge of a bit cell when the 
following two conditions are satisfied: 

(a) No data bit has been written in the praceding bit cell. 

(b) No data bit will be written in the present bit cell. 

In the MFM method, a clock bit at the leading edge of each bit cell is 
not always necessary as the clock will be regenerated in the FDD controlle 
Phase locked oscillator (PLO) is used to generate the clock and data 
window . 

The most appropriate window is lys for tl and 2ys for t2 in Fig. 220. 
The phase shall be locked so that the leading edge of the READ DATA 
pulse from the FDD locates at the center between two data window 
transitions. 



- 267 - 













1 


3it 


. cell (4U 


s) 












Bit 


cells ] 













1 


1 


1 


1 







MFM 
FDD 

MFM 


D C C 


D D D D 


WRITE/READ DATA 
data window 1 j 

4/3F <6us) 




1 
tl 




1 






lF(8us) 


i 
■ 






(5 


t2 


(2us) 






2F(4ys) 






0% of 


data 


t cycle) 













Note: The above timings (vis) are for FD-55A *v. F. Timings for FD-55G are 
a half of the indicated values. 

(Fig. 220) Bit correspondance and data window in the MFM method 

It is important for the PLO circuit to generate an accurate window as 
possible to obtain the widest window margin for data reading. It is 
therefore necessary that the PLO does not respond to bit shift caused 
by the read output peak shift from the magnetic head. It must be 
designed to respond slowly so that the data window will be phase-locked 
during several synchronizing bytes at the head of ID field or data 
field. 

Write pre-compensation is generally used as the active compensation 
method for the bit shift which contributes to the window margin 
effectively. Since the direction of bit shift can be predicted by the 
bit pattern, the position of the flux transition can be shifted in the 
opposite direction in anticipation. 

However, the degree of bit shift during read operation depends largely 
on the overall frequency characteristics of the FDD system and the most 
appropriate value of write pre-compensation should be determined for 
each FDD and disk. Large pre-compensation value results in undesirable 
effects such as an increase in bit shift at the outer tracks, decrease 



- 268 - 



in read output and a poorer S/N ratio due to the increased use of the 

bandwidth. Disk interchangeability suffers as a result. 

From these considerations it will be seen that bit shift should be 

reduced by increasing the frequency characteristics of the FDD and the 

minimum of write pre-compensation should be used. 

The simplest solution is to perform no write pre-compensation and the 

FDD has been designed to provide reliability and sufficiently wide window 

margin in this way. 

When you use the write pre-compensation, be careful to use the value 

less than ±250nsec for FD-55A ^ F and less than ±62. 5nsec for FD-55G, 

not to cause the undesirable effect by over compensation. 



- 269 - 



TEAC Corporation of America 

7733 Telegraph Rd., Montebello, CA 90640 

[21 3] 726-0303