Tandon TM848-1 Service manual

OEM
OPERATINGAND SERVICE MANUAL
TM848-1 ANDTM848-2 DISK DRIVES
48 TRACKSPERINCH
mn d u n coRpoRATIDN
20320 PRAIRIE STREET
CHATSWORTH, CA 91311
TELEPHONE NO.: [phone]
TWX NO.: 91 0 494 1 721
TEL.EX NO.: 194794
COPYRIGHT 1982 TANDON CORPORATION

The information contained in this document is the property of
Tandon Corporation. It may not be duplicated in full or part by
any person without prior written approval. The material in this
document is provided for informational purposes, and is subject
to change by Tandon Corporation.

TABLE OF CONTENTS
Section
Number Page
Number
Title of Section
SECTION I INTRODUCTION TO THE TM848 FAMILY OF DISK DRIVES
l.
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
1.10.1
1.1 0.2
1.1 0.3
1.11
1.12
1.13
1.14
1.15
1.1 5.1
1.1 5.2
1.1 5.3
1.1 5.4
1.1 5.5
1.1 6
1.1 6.1
1.1 6.2
1.17
1.1 7.1
1.1 7.2
1.1 7.3
1.18
1.19
1.1 9.1
1.1 9.2
1.1 9.3
1.1 9.4
1.1 9.5
1.1 9.6
1.1 9.7
1.1 9.8
1.1 9.9
1.1 9.1 0
1.1 9.1 1
1.1 9.1 2
1.1 9.1 3
1.1 9.1 4
1.1 9.1 5
1.1 9.1 6
1.1 9.1 7
Introduction.
Purpose Of The Drive
Physical Description of The Drive
Functional Description of The Drive
Diskettes
Mechanical and Electrical Sepcifications
Power Requirements
Interface Circuit Specifications
Incoming Inspection Checks and Procedures
Interface Connections
Mounting The Drive.
Hardware .
Dust Cover
Cooling System Requirements.... .. . . . . .. . .. . . . . . . . . . . . . .
Diskette Care, Handling and Storage .
Write Protect.
Operation of The Drive .....
Organization of The Drive
Components of The Drive
Index Pulse
Drive Status Logic .
Spindle Drive System
Positioner Control
Data Electronics
Interface Electronics
Interface Connector Pin Assignments, P13.
Power Connector Pin Assignments
Terminated Lines .
Input Line Terminations From Removable Resistor Pack.
Drive Select.
Program Shunt.
DS and HL Power Save Options
User-Selectable Options ..
Drive Select DS1-DS4.
Side Select Options Using Drive Select 1B-4B .
In Use From Drive Select .
In Use From Head Load ..
Ready Alternate Output Pad
Radial Ready
Ready Modified.
Radial Index
Index Alternate Output Pad
In Use Altenate Output Pad
Diskette Lever Lock Latch Option
Disk Change
Two-Sided Diskette Installed.
Stepper Power From Drive Select
Stepper Power From Head Load Line
Head Load Alternate Output Pad Option
Radial Head Load Signal Option.
. 1-1
. 1-1
. 1-1
. 1-1
. 1-2
I-2
. 1-2
. 1-2
. 1-2
1-5
. 1-5
. 1-6
. 1-6
.. 1-6
1-6
1-7
1-7
1-7
1-7
1-8
1-8
1-9
1-9
1-9
1-12
1-12
1-12
1-14
1-14
1-14
.. 1-14
1-17
1-1 7
1-18
1-18
1-18
1-18
1-18
1-1 9
. 1-19
1-1 9
1-20
1-20
1-20
1-20
1-20
1-21
1-21
1-21
1-21

Section
Number
1.1 9.1 8
1.1 9.1 9
1.1 9.20
1.1 9.21
1.1 9.22
S ECTION II MA INTEN A NC E CH E CKS AND ADJUST M E N T S
Page
Number
1-21
1-21
1-22
1-22
1-22
Title of Section
Inhibit Write When Write Protected
Allow Write When Write Protected .
Head Side Select Options S1 - S3
Spindle Motor Control Options M1 - M4
Motor Control Select Options MC1 - MC4.
2.
2.1
2.1.1
2.2
2.2.1
2.3
2.4
2.4.1
2.4.2
2.4.3
2.5
2.6
2.7
2.8
SECTION III PRIN TED CIRCUIT BOARD OPERATION
Introduction.
Spindle Drive Motor Checks and Adjustments...
Long-Term Drive Motor Speed Checks and Adjustments
Cats Eye Alignment Check and Adjustment
Cats Eye Alignment Check.
Head Carriage Adjustment
Index Sensor Checks and Adjustments
Index-To-Data Burst Checks
Index Sensor Adjustment
Index Pulse Width Check
Track 00 Sensor Check and Adjustment .
Amplitude Check.
Azimuth Check
Load Arm Adjustment
2-1
2-1
2-1
2 2
2-4
2-5
2-6
2-6
2-7
2-8
2-8
2-9
2-10
2-10
Introduction.
Physical Description of The Circuit Board.
Interface Electronics Specifications
Input Control Lines
Output Control Lines .......
.. 3-1
.. 3-1
3-1
3 2
.. 3-7
3.
3.1
3.2
3.3
3.4
SECTION IV T R OU B L E S H O O T ING GUIDE
4.
4.1
4.1
4.3
4.4
4.5
4.6
4.7
SECTION V REPL A C E M E NT PROCEDUR ES
Introduction.
Not Ready and/or No Index.
Will Not Seek or Restore....
Will Not Write
Will Not Read.
Activity L.E.D. Inoperative
No Track 00 Sensor Indication.
Drive Motor Will Not Start When Door Latched .
.. 4-1
.. 4-2
.. 4-2
.. 4-3
4-3
. 4-3
. 4-4
. 4-4
Introduction.
Drive Belt
Drive Motor.
Circuit Board.
Cone Assembly
Diskette Lever .
Bridge Assembly
Bezel
5-1
5-1
.. 5-2
5-3
.. 5-4
.. 5-6
5-6
.. 5-8
5.
5.1
5.2
5.3
5.4
5.5
5.6
5.7

Section
Number Page
Number
Title of Section
Activity L. E. D
Load Arm Assembly.
Track 00 Sensor Assembly.
Write Protect Sensor Assembly
Door Switch Assembly
Index Sensor Assembly.
Diskette Ejector Assembly.
Load Resistor Assembly
Stepper Band.
Stepper Motor Assembly
Head Carriage Assembly
5.8
5.9
5.10
5.1 1
5.1 2
5.1 3
5.1 4
5.1 5
5.'I 6
5.1 7
5.'I 8
APPENDIX I PRINTED CIRCUIT BOARD SCHEMATICS AND ASSEMBLY
5-9
5-1 0
. 5-10
5-1 1
5-1 2
. 5-12
5-1 4
5-1 5
5-1 6
. 5-18
5-1 9
DRAWINGS ..
11-1
APPENDIX II RECOMM E N D ED SPARE PARTS LIST..

LIST OF ILLUSTRATIONS
FIGURES
Figure
Number Page
Number
5-1
5-2
5-3
5-4
5-5
5-6
5-7
5-8
5-9
1-1
1-2
1-3
1-4
1-5
1-6
1-7
1-8
1-9
1-10
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
2-1 1
2-1 2
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-1 0
3-1 1
3-1 2
Title of Figure
TM848 Disk Drive Mounting Configuration.
TM848 Disk Drive Functional Block Diagram.
FM Recording Magnetization Profiles
Write Operation Timing Diagram
Read Timing Diagram.
Circuit Board Assembly
General Control and Data Timing Requirements
Radial Ready Installation .
Radial Index Installation
Radial Head Load Signal.
Circuit Board Assembly
Hub Center Line and Track Locations
Cats Eye Pattern.
Head Module Retaining and Cam Screws..
Index-to-Data Burst
Index Sensor's Retaining Screw and Adjustment.
Negative Going Pulse Width .
Track 00 Sensor ..
Optimum Head Azimuth Alignment.
Head Azimuth Alignment Acceptable Lower Limits
Head Azimuth Alignment Acceptable Upper Limits
Load Arm Adjustment, Front View
Printed Circuit Board.
Interface Configuration .
Select Lines Schematic Diagram.
Write Data Circuit Block Diagram
Trim Erase Diagram.
Side Select Schematic Diagram.
Index Schematic Diagram.
Waveform at Test Point 7, Soft Sectored.
Track 00 Schematic Diagram
Write Protect Schematic Diagram.
Read Circuit Block Diagram.
Read Data Schematic Diagram.
Drive Belt and Spindle
Drive Motor and Related Parts
Circuit Board Mounting Screws
Cone Assembly Key Parts
Cone Assembly Parts
Diskette Lever Key Parts
Diskette Lever Adjustment
Bridge Assembly Key Parts
Bridge Assembly Additional Key Parts
3-1
3-1
3-2
3-6
3-8
.. 3-9
3-1 1
. 3-1 1
3-1 2
3-1 3
.. 3-14
3-1 5
1-6
1-9
1-10
1-11
1-12
1-15
1-16
1-19
1-20
1-21
2-2
2-3
2-4
2-5
2-7
2-7
2-8
2-9
2-1 1
2-1 1
2-12
2-1 2
5-2
5-3
.. 5-4
.. 5-5
.. 5-5
5-6
5-7
5-7
5-8

FIGURES
Figure
Number
5-1 0
5-1 'I
5-1 2
5-1 3
5-14
5-1 5
5-1 6
5-1 7
Page
Number
5-8
.. 5-9
.. 5-10
5-1 1
5-1 2
.. 5-13
5-1 3
. 5-14
55-18
et Fi ere
T i t l e
Bezel and Related Parts
Activity L. E. D. Key Parts
Load Arm Assembly Key Parts
Track 00 Sensor Assembly Key Parts
Write Protect Sensor Assembly Key Parts..
Door Switch Assembly Key Parts .
Index Sensor Assembly Key Parts, Top View.
Index Sensor Assembly Key Parts, Bottom View.
Diskette Ejector Assembly Key Parts
Load Resistor Assembly and Key Parts
Stepper Band Key Parts
Stepper Band Additional Key Parts
Stepper Motor Assembly Key Parts......
Head Carriage Assembly Key Parts
TABLES
5-15
5-1 6
5-1 7
5-1 8
5-1 9
5-20
5-1 9
5-20
5-21
5-22
5-23
Table
Number Page NumberTitle of Table
Mechanical and Electrical Specifications
Power Requirements
Interface Connector Pin Assingments..
Power Connector Pin Assignments
Options
Drive Interface Lines and Pin Connectors
Stepper Logic Truth Table .
1-3
1-4
1-13
1-14
1-17
3-3
3-5
1-1
1-2
1-3
1-4
1-5
3-1
3-2

SECTION I
INTRODUCTION TO THE TM848 FAMILY OF DISK DRIVES
INTRODUCTION
This section contains a description of the physical and functional specifications for the TM848-1 and-
2 disk drives, 48 tracks per inch (TPI), manufactured by Tandon Corporation.
1.1 PURPOSE OF THE DRIVE
The drive is an eight-inch disk memory designed for random access data entry, storage, and retrieval
applications. These applications typically are intelligent terminal controllers, microcomputers, word
processing systems, data communications systems, error logging, microprogram loading, point-of-
sale terminals, and Winchester back ups.
The drive is capable of recording and reading digital data, using FM, and MFM.
PHYSICAL DESCRIPTION OF THE DRIVE1.2
The drive can be mounted in any vertical or horizontal plane. However, when mounted horizontally,
the printed circuit board must be up.
The spindle is belt driven by a brushless D.C. motor with an integral tachometer. The servo control
circuit, suitably sized pulleys, and the tachometer control the speed of the spindle. The Read/Write,
double-sided head assembly is positioned by means of a stepper motor, split band, and a pulley.
The Read/Write/Erase head assembly is a glass-bonded manganese/zinc ceramic structure. It has a
life in excess of 20,000 hours.
For diskette loading, operator access is provide via a slot located on the front of the drive.
The electronic components of the drive are mounted on a circuit board assembly located in the
chassis. Power and interface signals are routed through connectors that plug into the back of the drive.
1.3 FU NC TIONAL DESCRIPTION OF THE DRIVE
The drive is fully self-contained. It requires no operator intervention during normal operation. The
drive consists of a spindle drive system, a head positioning system, and a read/write/erase system.
The TM848-1 is a single-sided drive. The TM848-2 is a double-sided drive. The only difference
between the two drives is the number of heads. The circuit board is identical in both models.
When the diskette lever is opened, access is provided for the insertion of a diskette. The diskette is
accurately positioned by plastic guides. The disk position is ensured by the backstop and disk ejector.
Closing the diskette lever activates the cone/clamp system, resulting in centering of the diskette and
clamping of the diskette to the drive hub. The drive hub is driven at a constant speed of 360 RPM by a
servo-controlled brushless D. C. motor. The head is loaded into contact with the recording medium
whenever the diskette lever is latched.
1-1

The head is positioned over the desired track by means of a stepper motor/band assembly and its
associated electronics. This positioner employs a 3.6 degree rotation to cause a one-track linear
movement. When a write-protected diskette is inserted into the drive, the Write Protect sensor
disables the write electronics of the drive, and a Write Protect status output signal is available to the
interface.
When performing a write operation, a 0.013-inch wide (nominal) data track is recorded. This track is
then tunnel erased to 0.012 inch (nominal).
Data recovery electronics include a low-level head amplifier, a differentiator, a zero crossing
detector, and digitizing circuits.
No data-clock separation is provided.
In addition, the drive is supplied with the following sensor systems:
1. A track 00 sensor that senses when the Head Carriage Assembly is positioned at Track 00.
2. The two index sensors, each of which consists of a L.E.D. light source and a phototransistor,
are positioned so that a signal is generated when a index hole is detected. The drive can
determine whether a single- or double-sided diskette is installed. This output signal is present
at the interface.
3. The Write Protect sensor disables the drive's write electronics whenever a write-enable tab is
removed from the diskette (see Section 1.12).
1.4 DISKETTES
The drive uses a standard eight-inch diskette. Diskettes are available with a single index hole or with
index and sector holes. They also are available double- or single-sided.
Single index hole diskettes are used when sector information is pre-recorded on the diskette (soft
sectoring). Multiple index hole diskettes provide sector pulses by means of the index sensor and
electronics (hard sectoring).
1.5 M EC H AN ICAL AND ELECTRICAL SPECIFICATIONS
The mechanical and electrical specifications of the drive are listed in Table 1-1.
1.6 POWER REQUIREMENTS
The power requirements of the drive are listed in Table 1-2.
1.7 INTERFACE CIRCUIT SPECIFICATIONS
The interface circuits are designed so that a disconnected wire results in a false signal.
Levels:
True =+0.4 V, maximum
False =+2.4 V, minimum
1.8 IN C O M ING INSPECTION CHECKS AND PROCEDU RES
There are two kinds of recommended incoming inspection checks and procedures: static and
dynamic ones.
The static incoming inspection checks include the minimum steps that should be taken to ensure
that the drive is operational when received.
1-2

TABLE 1-1
MECHANICAL AND ELECTRICAL SPECIFICATIONS
MECHANICAL
Height: 2.30 inches
Width: 8 inches Length: 13.125 inches behind front panel
Weight: 5.5 pounds
ELECTRICAL
+ 5 V D. C. Power:
+24 V D. C. Power:
Selected Motor On:
Dese lected:
SpindleMotor:
Start Current Surge:
ENVIRONMENTAL
Operating Temperature:
Storage Temperature:
Wet Bulb Temperature:
Noncondensing Operating Humidity:
RELIABILITY
+5 volts 2 5 percent, 0.75 amp typical
+24 volts+ 10 percent
0.75 amp typical
0.20 amp typical
0.40 amp typical
2.5 amps, 400 msec on, 24 volts total
4.4'C to 46'C (40 F to 115 F)
— 40'C to 71'C ( — 40 F to 160 F)
26 C (78'F) maximum
20-to-80 percent
MTBF:
MTTR:
Error Rates:
Soft Read:
Hard Read:
Seek Errors:
PERFORMANCE
Head Wear Guarantee:
Number of Tracks:
Track-To-Track Access Time:
Head Settling Time:
Average Access Time,
including head settling time:
Motor Start Time:
Disk Rotational Speed:
Instantaneous Speed Variation:
Flux Changes Per Inch, Inside Track:
Transfer Rates:
Linformatted Recording Capacity:
1 in 10' bits
1 in 10" bits
1 in I 0' seeks
10,000 power-on hours
30 minutes
IBM Format Recording Capacity:
15,000 media hours
77 for TM848-1; 154 for TM848-2, 77 per surface
3 milliseconds
15 milliseconds
91 milliseconds
700 milliseconds
360 RPM
+ 1.0 percent
6536 FCI, Side 0, both models;
6818 FCI, Side 1, TM848-2 only
250K BPS single density,500K BPS
double density
0.8 MBytes per disk, single density,
double-sided drive
1.6 MBytes per disk, double density,
double-sided drive
0.6 MBytes, single density, double-sided
drive
1.2 MBytes, double density, double-sided
drive
FM single density, MFM double densityRecording Method:
1-3

TABLE 1-2
POWER REQUIREMENTS
1. + 5 Volts:
2. +24 Volts: After motor start interval
0.70 Amps typical
Spindle Motor 0.35 Amps typical
Stepper Motor 0.40 Amps typical
Electronics 0.17 Amps typical
Total 0.92 Amps typical
3. +24 Volts: During motor start interval
a. Configured for stepper motor enabled during motor start.
2.5 Amps typical surge.
2.5
2.0
1.5
1.0
0.5
100 200 300 400 600500
TIME (MILLISECONDS)
b. Configured for stepper motor disabled until motor comes up to
speed. 2.1 Amps typical surge.
2.5
2.0 STEPPER MOTOR
ENABLED
1.5
1.0
0.5
200 300 400 500 600
100
TIME (MILLISECONDSI
1-4

A. Inspect the shipping package for obvious damage.
B. Open the shipping container, and remove the drive.
C. Inspect the drive's overall appearance. Ensure that there are no scratches on the bezel.
D. Ensure that all internal connectors are seated properly.
E. Turn the diskette lever counterclockwise, and remove the shipping diskette.
F. Insert a blank diskette, close, and then open the diskette lever. The diskette should eject.
G. Insert a blank diskette, and manually turn the spindle pulley. It should rotate freely.
The dynamic incoming inspection procedures include:
A. Connect the drive to an exerciser or computer tester capable of seeking, writing, and reading.
B. Power up the test equipment, and apply power to the drive.
C. Select the drive, and ensure that the Activity L. E. D. located on the bezel illuminates.
D. Insert a work diskette and write/verify from Track 00 to Track 76. Ensure that there are no
errors.
E. Insert a diskette written previously on another drive. Read this diskette, and ensure that there
are no data errors. If excessive errors occur, check the diskette on the drive on which it was
written.
F. If the drive passes all the checks listed above, it is operational. If not, review Section II.
INTERFACE CONNECTIONS1.9
Signal connections for the drive are made via a user-supplied 50-pin, flat ribbon connector (3M
Scotchflex 3415). This connector mates directly with the circuit board connector at the rear of the
drive. The D. C. power connector is a six-pin connector (Amp Mate-N-Lok Part Number 1-480270-0),
which mates with the connector at the rear of the drive.
The signal connector harness should be of the flat ribbon or twisted pair type, have a maximum length
of ten feet, and have a 22-to-28 gauge conductor compatible with the connector that is to be used.
Power connections should be made with 18-AWG cable, minimum.
1.10 MO UNTING THE DRIVE
The drive has been designed to mount in any plane, i.e.: upright, horizontal, or vertical. The only
restriction is that the printed circuit board side of the chassis must be uppermost when the drive is
mounted horizontally. Eight holes are provided for mounting: two on each side and four on the bottom
of the housing (see Figure 1-1). The two on each side are tapped for 8-32 screws. The four mounting
holes on the bottom require 8-32 thread forming screws.
Optional straps are available to permit attaching two drives together for installation in standard width
drive openings.
1-5

0o
6-32 THD
THRLI 4 PL
(2 EA. SIDE) 0
8.00
13.33
3.50 0'0 149 DIA. TOP X
1 56 DIA. BOTTOM X
.430 DP.
4 PL
O.P
3pp I 20
6~ I
8 550 1 60
2.300
NOTES. DIMENSIONS GIVEN IN INCHES.
Figure 1-1
TM848 Disk Drive Mounting Configuration
1.10.1 Hardware
The drive is manufactured with certain critical internal alignments that must be maintained. Hence, it
is important that the mounting hardware does not introduce significant stress on the drive.
A three-part mounting scheme is recommended. Any mounting scheme in which the drive is part of
the structural integrity of the enclosure may cause equipment operating problems and should be
avoided. In addition, the mounting scheme should allow for adjustable brackets or incorporate
resilient members to accommodate tolerences.
1.10.2 Dust Cover
The design of an enclosure should incorporate a means to prevent contamination from loose items
e.g., dust, lint, and paper since the drive does not have a dust cover.
1.10.3 Cooling System Requirements
Heat dissipation from a single drive is normally 30 watts (102) Btu/Hr.) under high line conditions.
When the drive is mounted so that the components have access to the free flow of air, normal
convection cooling allows operation over the specified temperature range.
When the drive is mounted in a confined environment, air flow must be provided to maintain specified
air temperatures in the vicinity of the motors, the circuit board, and the diskette.
1.1 1 D I SK ETTE CARE, HAND LI NG, AND STORAGE
It is important that the diskette be cared for, handled, and stored properly so that the integrity of the
recorded data is maintained. A damaged or contaminated diskette can impair or prevent recovery of
data, and can result in damage to the read/write heads of the drive.
1-6

The following list contains information on how the diskette can be cared for, handled, and stored.
1. Keep the diskette away from magnetic fields.
2. Do not touch the precision surface of the diskette with fingers.
3. Insert the diskette carefully into the drive until the backstop is encountered.
4. Do not bend or fold the diskette.
5. Put the diskette into its jacket when it is not in use.
6. Store the diskette at temperatures between 10'C and 52'C or 50'F and 125'F.
1.12 WRITE PROTECT
The drive is equipped with a Write Protect Sensor Assembly. This sensor operates in conjunction with
a diskette that has a slot cut in the protective jacket.
When the slot is uncovered, the diskette is write protected. The slot must be covered to write on the
diskette. An option is available on the board for defeating the write protect sensor.
1.13 OPERATION OF THE DRIVE
The drive consists of the mechanical and electrical components necessary to record and to read
digital data on a diskette. User-provided D.C. power at+24 volts and+5 volts is required for operation
of the drive.
1.14 ORGANIZATION OF THE DRIVE
All electrical subassemblies in the drive are constructed with leads that terminate in multipin
connectors, enabling the individual assemblies to be removed.
The heads are connected to the circuit board via cables that terminate in five-pin female connectors
and their associated male sockets that are located in close proximity to the read/write data
electronics.
Interface signals and power are provided via connectors at the rear of the drive.
1.15 COMPONENTS OF THE DRIVE
The drive consists of six functional groups:
1. Index Pulse Shaper
2. D rive Status Logic
A. Write Protect
B. Track 00 Sensor
C. Double-sided Disk
D. Ready
E. Disk Change
1-7

3. Spindle Drive Control
4. Carriage Position Control
5. Write/Erase Control
6. Read Amplifier and Digitizer
Figure 1-2 is a functional block diagram of the drive. It should be referred to in conjunction with the
following sections. The data in the ensuing figures is primarily represented in simplified form.
1.15.1 Index Pulse
An index pulse is provided to the user system via the index pulse interface line. The index circuitry
consists of an index L. E. D., an index phototransistor, and a pulse shaping network. As the index hole
in the disk passes an index L. E. D. phototransistor combination, light from the L. E. D. strikes the index
phototransistor, causing it to conduct. The signal from the index phototransistor is passed on to the
pulse shaping network, which produces a pulse for each hole detected. This pulse is presented to the
user on the index pulse interface line.
1.15.2 DriveStatus Logic
There are five drive status logic lines: Write Protect, Track 00 Sensor, Two-Sided Ready and Disk
Change.
A. Write Protect
A write protect signal is provided to the user's system via the write protect interface line. The
write protect circuitry consists of a write protect sensor and circuitry that routes the signal
that is produced.
When a write protected diskette is inserted in the drive, the sensor is activated and the logic
disables the write electronics and supplies the status signal to the interface.
B. Track 00 Sensor
The level on the Track 00 interface line is a function of the position of the head assembly.
When the head is positioned at Track 00 and the stepper motor is at the home position, a true
(low) level signal is generated at the interface.
C. Two-Sided Disk
This signal is low(true) when the drive is selected and has detected the presence of the Index
Two hole in the diskette currently installed.
D. Ready
This signal is true when Drive Select is low (true) if the spindle drive is up to speed and the
drive is ready to read and write.
E. Disk Change
This signal is true when Drive Select is low (true) if the diskette lever has been moved to the
open position after the previous drive select went false.
1-8

1.15.3 Spindle Drive System
The spindle drive system consists of a spindle assembly driven through a drive belt by a brushless
D.C. motor/tachometer.
The servo electronics required for speed control are located on the printed circuit board.
The control circuitry contains an interface control line. When the drive motor control interface line is
false (high), the drive motor is allowed to come up to speed.
READY
INDEX SENSOR
L.E.D.'S ~ CONTROL
LOGIC INDEX
DISK CHANGE
TWO SIDED
D.C.
STEPPER
MOTOR WRITE PROTECT
TRACK 00
WRITE PROTECT
SENSOR+
L.E.D. IN USE
INDEX DETECTORS
SIDE SELECT
HEAD CARRIAGE
AND STEPPER
BAND
ASSEMBLY
WR ITE
PROTECT
DETECTOR DRIVE SELECT
SPINDLE
MOTOR
CONTROL
MOTOR CONTROL
D.C. DRIVE
MOTOR
WRITE GATE
WRITE DATAWRITE
LOGIC CURRENT SWITCH
READ
LOGIC READ DATA
DIRECTION
STEPPER
MOTOR
CONTROL STEP
Figure 1-2
TM848 Disk Drive Functional Block Diagram
1.15 4 Positioner Control
The head positioning system uses a bipolar-driven motor drive, which changes one phase for each
track advancement of the read/write carriage. In addition to the logic necessary for motor control, a
gate is provided that inhibits positioner motion during a write operation.
1.15.5 Data Electronics
Information can be recorded on the diskette by using a double-frequency code. Figure 1-3 illustrates
the magnetization profiles in each bit cell for the number sequence shown for FM recording.
1-9

BIT PATTERN~ BIT CELLP+ )010
I
I
I
I
C)D C
I)
II
II I ))) )
)
0I
I
I
I
1
I
I )
I )
MAGNETIZATION
WRITE DATA
D /C
I
II
I
D IC
Ic I c
I I
D C
I
II
IIII I
MAGNETIC ELEMENTS NS S N N S SS S N N S S
II ) I
III) ) I
II • I ) I s I ) I I
Figure 1-3
FM Recording Magnetization Profiles
The erase gaps provide a guard band on either side of the recorded track.
All signals required to control the data electronics are provided by the user system and are shown in
the TM848 drive functional block diagram (see Figure 1-2). These control signals are:
1. Select
2. Write Gate
3. Write Data
4. Side Select
5. Write Current Switch
Composite read data is sent to the user system via the Read Data interface line.
A. Data Recording
The write electronics consist of a switchable write current source, a write waveform
generator, an erase current source, the trim erase control logic, and the head selection logic
(see Appendix I).
The read/write winding on the head is center-tapped. During a write operation, current from
the write current source flows in alternate halves of the winding, under control of the write
waveform generator.
The conditions required for recording, i.e. drive ready must be established by the user's
system, as follows:
1. Drive speed stabilization occurs 700 milliseconds after the drive motor is started.
2. Subsequent to any read/write operation, the positioner must be allowed to settle. This
requires 18 milliseconds maximum after the last step pulse is initiated, i.e., 3 milliseconds
for the step motion and 15 milliseconds for settling.
3. The foregoing operations can be overlapped, if required.
Figure 1-4 illustrates the timing diagram for a write operation. At t = 0, when the unit is ready,
the write gate interface line goes true. This enables the write current source. Write current is
switched via the write current switch interface line to a lower value by the user's controller at
Track 43.
1-10

The Trim Erase control goes true 190 microseconds after the Write Enable interface line
since the trim erase gaps are behind the read/write gap. It should be noted that this value is
optimized between the requirements at Track 00 and at Track 76, so that the effect of the trim
erase gaps on previous information is minimized.
Figure 1-4 shows the information on the write data interface line and the output of the write
waveform generator, which toggles on the leading edge of every write data pulse.
A maximum of 4 microseconds between write gate going true and the first write data pulse is
only required if faithful reproduction of the first write data transition is signifcant.
At the end of recording, at least one additional pulse on the write data line must be inserted
after the last significant write data pulse to avoid excessive peak shift effects.
NOTE 1
I
NOTE 2
WRITE GATE 190 u sec I~5 0 u sec~I
TRIM E:RASE
INTERNAL WRITE
BUSY I
WRITE DATA II
NOTE 2 I
WRITE
WAVEFORM
GENERATOR I
II
WRITE CURRENT - NOTE 3
NOTE 4Q
1=0 NOTES: 1, T = 0 700 MILLISECONDS AFTER DRIVE MOTOR
STARTS OR 20 MILLISECONDS AFTER LAST STEP
PULSE, WHICHEVER IS THE LATEST TIME.
3. 10 MA PEAK TO PEAK, TRACK 0 TO
TRACK 42; 7.5 MA PEAKTOPEAK
TRACK 43 TO TRACK 77.
2. UNSYCHRONIZED 4. 2 USEC MINIMUM
4 USEC MAXIMUM
Figure 1-4
Write Operation Timing Diagram
The duration of a write operation is from the true going edge of write gate to the false going edge of
erase. This is indicated by the internal write busy waveform shown (see Figure 1-4).
The Read electronics consist of:
1, Read Switch/Side Select
2. Read Preamplifier
3. Filter
4. Differentiatior
5. Time Domain Filter and Digitizer
The read switch is used to isolate the read amplifier from the voltage excursion across the head
during a write operation. The side select is used to enable one of the read/write/erase heads.
The drive must be in a ready condition before reading can begin. As with the data recording operation,
this ready condition must be established by the user system. ln addition to the requirements
established in this section, a period of 100 microseconds is necessary after a trim erase operation
occurs to allow the read amplifier to settle after the transient caused by the read switch returning to
the read mode. 1-11

The output signal from the read/write head is amplified by a read preamplifier and filtered by a low-
pass linear phase filter to remove noise (see Figure 1-5). The linear output from the filter is passed to
the differentiator, which generates a wave form whose zero crossovers correspond to the peaks of the
Read signal. This signal is then fed to the zero crossing detector and digitizer.
I
I I
I
I
I
II
II
LINEAR OUTPUT FROM FILTER I
III
OUTPUT FROM DIFFERENTIATOR
I I
I
I
I
I
I
DIFFERENTIAL DROOP
READ DATA INTERFACE I I I
I I
IfI
III
I > I
I=o
Figure 1-5
Read Timing Diagram
Note
T = 0 is defined as 250 milliseconds after drive motor starts, or 20 milliseconds after a step
command, or 100 microseconds after termination of write busy, whichever is the latest time.
The zero crossover detector and digitizer circuitry generate a 200 nanosecond read data pulse,
corresponding to each peak of the read signal. The composite read data signal is sent to the user
system via the read data interface line.
1.16 I NTERFACE ELECTRONICS
All interface signals are TTL compatible. Logic true (low) is +0.4 volt maximum, logic false (high) is
+2.4 volts minimum. The maximum interface cable length is ten feet. It is recommended that the
interface cable be flat ribbon cable that has a characteristic impedence of 100 ohms.
1.16.1 Interface Connector Pin Assignments, P13
The interface connector pin assignments, P13, are listed in Table 1-3.
1.16.2 Power Connector Pin Assignments
The power connector pin assignments are listed in Table 1-4.
1-12

TABLE 1-3
IN TE R FAC E CO N N ECTO R P IN ASS IG NM ENTS
Ground Pin Number
1
35 246
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
~
si nal
Write Current Switch
Motor Off Control 1
Motor Off Control 2
Motor Off Control 3
Two Sided (option) (Model TM848-2 only)
Disk Change (option)
Side Select (Model TM848-2 only)
Activity Indicator (option)
Head Load
Index
Ready
Motor Off Control 4
Drive Select 1 (Side Select Option, TM848-2 only)
Drive Select 2 (Side Select Option, TM848-2 only)
Drive Select 3 (Side Select Option, TM848-2 only)
Drive Select 4 (Side Select Option, TM848-2 only)
Direction Select (Side Select Option, TM848-2 only)
Step
Write Data
Write Gate
Track 00
Write Protect
Read Data
Alternate I/O
Alternate I/O
7
9
11
13
'15
'17
19
.'21
,'23
.'25
27
29
31
33
35
37
39
41
43
45
47
49