Tandon TM848-1 Service manual

OEM
OPERATING AND SERVICE MANUAL
TM848-1 AND TM848-2 DISK DRIVES
48 TRACKS PER INCH
'anCion
CORPORATION
20320 PRAI RI ESTREET
CHATSWORTH, CA 91311
TELEPHONE NO.: [phone]
TWX NO.: 910 494 1721
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.

Sectoon
Number
SECTION I
TABLE OF CONTENTS
Title of Section
INTRODUCTION TOTHETM848 FAMILYOF DISKDRIVES
Page
Number
1.
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
1.10.1
1.10.2
1.10.3
1.11
1.12
1.13
1.14
1.15
1.15.1
1.15.2
1.15.3
1.15.4
1.15.5
1.16
1.16.1
1.16.2
1.17
1.17.1
1.17.2
1.17.3
1.18
1.19
1.19.1
1.19.2
1.19.3
1.19.4
1.19.5
1.19.6
1.19.7
1.19.8
1.19.9
1.19.10
1.19.11
1.19.12
1.19.13
1.19.14
1.19.15
1.19.16
1.19.17
Introduction 1-1
Purpose Of The Drive 1-1
Physical Description of The Drive 1-1
Functional Description of The Drive 1-1
Diskettes 1-2
Mechanical and Electrical Sepcifications 1-2
Power Requirements 1-2
Interface Circuit Specifications 1-2
Incoming Inspection Checks and Procedures 1-2
Interface Connections 1-5
Mounting The Drive .. " " , 1-5
Hardware "1-6
Dust Cover. 1-6
Cooling System Requirements 1-6
Diskette Care, Handling and Storage 1-6
Write Protect. 1-7
Operation of The Drive 1-7
Organization of The Drive 1-7
Components of The Drive '" 1-7
Index Pulse " , " 1-8
Drive Status Logic " 1-8
Spindle Drive System 1-9
Positioner Control " 1-9
Data Electronics 1-9
Interface Electronics " '" 1-12
Interface Connector Pin Assignments, P13 1-12
Power Connector Pin Assignments 1-12
Terminated Lines 1-14
Input Line Terminations From Removable Resistor Pack 1-14
Drive Select. 1-14
Program Shunt 1-14
DS and HL Power Save Options 1-17
User-Selectable Options 1-17
Drive Select DS1--DS4 , 1-18
Side Select Options Using Drive Select 18--48 1-18
In Use From Drive Select 1-18
In Use From Head Load " '" 1-18
Ready Alternate Output Pad 1-18
Radial Ready .. '" '" 1-19
Ready Modified 1-19
Radial Index " 1-19
I ndex Alternate Output Pad 1-20
In Use Altenate Output Pad 1-20
Diskette Lever Lock Latch Option 1-20
Disk Change 1-20
Two-Sided Diskette Installed 1-20
Stepper Power From Drive Select 1-21
Stepper Power From Head Load Line ,1-21
Head Load Alternate Output Pad Option 1-21
Radial
Head Load Signal Option 1-21

Section
Number
Title of Section
Page
Number
1.19.18
1.19.19
1.19.20
1.19.21
1.19.22
Inhibit Write When Write Protected ,1-21
Allow Write When Write Protected 1-21
Head Side Select Options S1 - S3 , 1-22
Spindle Motor Control Options M1 - M4 1-22
Motor Control Select Options MC1 - MC4 1-22
SECTION II MAINTENANCE CHECKS AND ADJUSTMENTS
2. Introduction 2-1
2.1 Spindle Drive Motor Checks and Adjustments 2-1
2.1.1 Long-Term Drive Motor Speed Checks and Adjustments , 2-1
2.2 Cats Eye Alignment Check and Adjustment 2-2
2.2.1
Cats Eye Alignment Check 2-4
2.3
Head Carriage Adjustment 2-5
2.4
Index Sensor Checks and Adjustments 2-6
2.4.1 Index-To-Data Burst
Checks 2-6
2.4.2
Index Sensor Adjustment ,2-7
2.4.3
Index Pulse Width Check 2-8
2.5 Track
00 Sensor Check and Adjustment 2-8
2.6
Amplitude Check 2-9
2.7
Azimuth Check 2-10
2.8 Load Arm Adjustment 2-10
SECTION III
PRINTED CIRCUIT BOARD OPERATION
3.
3.1
3.2
3.3
3.4
Introduction 3-1
Physical Description of The Circuit Board 3-1
Interface Electronics Specifications 3-1
Input Control Lines 3-2
Output Control Lines 3-7
SECTION IV TROUBLESHOOTING GUIDE
4.
4.1
4.1
4.3
4.4
4.5
4.6
4.7
Introduction " " ., " .. 4-1
Not Ready and/or No Index , .. 4-2
Will
Not Seek or Restore 4-2
Will
Not Write 4-3
Will
Not Read 4-3
Activity L.E.D. Inoperative 4-3
No Track 00 Sensor Indication 4-4
Drive Motor Will Not Start When Door Latched 4-4
SECTION VREPLACEMENT PROCEDURES
5. Introduction 5-1
5.1 Drive Belt 5-1
5.2 Drive Motor 5-2
5.3
Circuit Board 5-3
5.4
Cone Assembly 5-4
5.5
Diskette Lever , " 5-6
5.6
Bridge Assembly 5-6
5.7 Bezel 5-8
ii

Section
Number
Title of Section
Page
Number
5,8
5,9
5,10
5,'11
5,12
5,13
5,'14
5,'15
5,'16
5,'17
5.'18
Activity L, E, D",. , " , " , ., ", """ , . , ., , . " ., ., ", .. , . , , , . , ., " ", ., ,5-9
Load Arm Assembly, ., .. , , , , ., , , . , ,, , , , ,. , ... , , , , ., . , , . , , , , , ., , . , . , .. , . , . 5-10
Track 00 Sensor Assembly, , , , ,, , , . , ,, , . , ,, ., , . , ., . , , .. , .. , , . , . , , . , , , . 5-10
Write Protect Sensor Assembly, , , , , ., , , ,, , , ,. , , ., . , .. , .. , 5-11
Door Switch Assembly .. , , , , .. , , . , , , , , , , 5-12
Index Sensor Assembly. , ., .. , , , . , ., , " .. , 5-12
Diskette Ejector Assembly ,,,,, .. , , , , , , 5-14
Load Resistor Assembly, , , , , . ,, , , . ,, .. , , , . , 5-15
Stepper Band, , , , , , , , , , , .. ,, , 5-16
Stepper Motor Assembly , ., , .. , , , ., , , , 5-18
Head Carriage Assembly"" .. "", .. " , , , 5-19
APPENDIX IPRINTED CIRCUIT BOARD SCHEMATICS AND ASSEMBLY
DRAWiNGS"", ".,."", , " , , 1-1
APPENDIX II RECOMMENDED SPARE PARTS LIST , " .. , , 11-1
iii

LIST OF ILLUSTRATIONS
FIGURES
Figure
Number
Title of Figure
Page
Number
1-1 TM848 Disk Drive Mounting Configuration "1-6
1-2
TM848 Disk Drive Functional Block Diagram "1-9
1-3 FM
Recording Magnetization Profiles 1-10
1-4 Write Operation Timing Diagram 1-11
1-5 Read Timing Diagram
1-12
1-6 Circuit Board Assembly " " ' 1-15
1-7 General Control and Data Timing Requirements , .. , 1-16
1-8 Radial Ready Installation .. " " " 1-19
1-9 Radial I ndex Installation 1-20
1-10 Radial Head Load Signal. 1-21
2-1 Circuit Board Assembly 2-2
2-2
Hub Center Line and Track Locations 2-3
2-3 Cats Eye Pattern 2-4
2-4
Head Module Retaining and Cam Screws 2-5
2-5
Index-to-Data Burst .. " , 2-7
2-6
Index Sensor's Retaining Screw and Adjustment. 2-7
2-7 Negative Going Pulse Width 2-8
2-8
Track 00 Sensor 2-9
2-9
Optimum Head Azimuth Alignment. 2-11
2-10 Head Azimuth Alignment Acceptable Lower Limits 2-11
2-11
Head Azimuth Alignment Acceptable Upper Limits ,2-12
2-12
Load Arm Adjustment, Front View 2-12
3-1 Printed Circuit Board 3-1
3-2 Interface Configuration 3-1
3-3 S~lect Lines Schematic Diagram 3-2
3-4 Write Data Circuit Block Diagram 3-6
3-5 Trim Erase Diagram 3-8
3-6 Side
Select Schematic Diagram 3-9
3-7
Index Schematic Diagram ,3-11
3-8 Waveform
at Test Point 7, Soft Sectored 3-11
3-9
Track 00 Schematic Diagram 3-12
3-10 Write Protect Schematic Diagram " " 3-13
3-11 Read Circuit Block Diagram " " 3-14
3-12 Read Data Schematic Diagram 3-15
5-1 Drive Belt and Spindle 5-2
5-2 Drive
Motor and Related Parts 5-3
5-3
Circuit Board Mounting Screws "5-4
5-4
Cone Assembly Key Parts 5-5
5-5
Cone Assembly Parts 5-5
5-6
Diskette Lever Key Parts 5-6
5-7
Diskette Lever Adjustment 5-7
5-8
Bridge Assembly Key Parts "5-7
5-9
Bridge Assembly Additional Key Parts "5-8
iv

Figure
Number
Title of Figure
FIGURES
Page
Number
5-10 Bezel and Related Parts 5-8
5-1 "I Activity L. E. D. Key Parts 5-9
5-12 Load Arm Assembly Key Parts 5-10
5-13 Track 00 Sensor Assembly Key Parts 5-11
5-14 Write Protect Sensor Assembly Key Parts 5-12
5-15
Door Switch Assembly Key Parts 5-13
5-16
Index Sensor Assembly Key Parts, Top View 5-13
5-17 Index Sensor Assembly Key Parts, Bottom View 5-14
5
5-18 Diskette Ejector Assembly Key Parts , 5-15
5-19 Load Resistor Assembly and Key Parts 5-16
5-20
Stepper Band Key Parts 5-17
5-21 Stepper Band Additional Key Parts 5-18
5-22 Stepper Motor Assembly Key Parts 5-19
5-23 Head Carriage Assembly Key Parts 5-20
TABLES
Table
Number
Title of Table
Page
Number
1-1
1-2
1-3
1-4
1-5
3-1
3-2
Mechanical and Electrical Specifications 1-3
Power Requirements 1-4
Interface Connector Pin Assingments 1-13
Power Connector Pin Assignments 1-14
Options 1-17
Drive Interface Lines and Pin Connectors '" , 3-3
Stepper Logic Truth Table 3-5
v

SECTION I
INTRODUCTION TO THE TM848 FAMILY OF DISK DRIVES
1. INTRODUCTION
This section contains a description of the physical and functional specifications forthe 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.
1.2 PHYSICAL DESCRIPTION
OF THE DRIVE
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 apulley.
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 signalsare routed through connectors that plug into the back ofthe drive.
1.3 FUNCTIONAL 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, ahead 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 a3.6 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 alow-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 aL.E.D. light source and a phototransistor,
are positioned so that asignal is generated when a index hole is detected. The drive can
determine whether asingle- or double-sided diskette is installed.This output signalis 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. Diskette$ are available with a single index hole orwith
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
MECHANICAL 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 afalse signal.
Levels:
True =
+0.4 V, maximum
False =
+2.4 V, minimum
1.8
INCOMING INSPECTION CHECKS AND PROCEDURES
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
ELECTRICAL
+ 5 V
D. C. Power:
+24 V D. C. Power:
Selected Motor On:
Deselected:
Spindle Motor:
Start Current Surge:
ENVIRONMENTAL
Operating Temperature:
Storage Temperature:
Wet Bulb Temperature:
Noncondensing Operating Humidity:
RELIABILITY
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:
I
nstantaneous Speed Variation:
Flux
Changes Per Inch, Inside Track:
Transfer Rates:
Unformatted Recording Capacity:
IBM
Format Recording Capacity:
Recording Method:
1-3
Length: 13.125 inches behind front panel
Weight: 5.5 pounds
+5 volts ±5percent, 0.75 amp typical
+24 volts ± 10 percent
0.75 amp typical
0.20 amp typical
OAO 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
10,000 power-on hours
30 minutes
1in 10
9
bits
1in 10
12
bits
1in 10
6
seeks
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 M Bytes 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 density

TABLE 1-2
POWER REQUIREMENTS
1.
+5 Volts:
0.70 Amps typical
2.
+24 Volts: After motor start interval
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
(j)
2.0
a..
~
~
~
1.5
z
w
a:
a:
1.0
::::>
()
0.5 "\..
100 200 300 400
TIME (MILLISECONDS)
b. Configured for stepper motor disabled until motor comes up to
speed. 2.1 Amps typical surge.
500
600
600
500
400
300
200
100
ISTEPPER MOTOR
ENABLED
"V
~
I
•
2.5
en
2.0
a..
~
~
~
1.5
z
w
a:
a:
1.0
::::>
()
0.5
TIME (MILLISECONDS)
1-4

A. Inspect the shipping package for obvious damage.
B. Open the shipping container, and remove the drive.
C. I nspect 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. I nsert a work diskette and write/verify from Track 00 to Track 76. Ensure that there are no
errors.
E. I nsert 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.
1.9 INTERFACE
CONNECTIONS
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 asix-pin connector (Amp Mate-N-Lok Part Number 1-480270-0),
which mates with the connector at the rear of the drive.
Thesignal
connector harness should be of the flat ribbon ortwisted pair type, haveamaximum 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
MOUNTING THE DRIVE
The drive has
been designed to mount in any plane, Le.: 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 areavailable to permit attaching two drives together for installation in standard width
drive openings.
1-5

---
0"
~- °
F_}- 0r.!l\'l. ~1P.iI1r=--'t1
13.33
[( JI
~- -··------8.550----~
e ~ .. +
6-32 THO
THRU 4PL
(2 EA. SIDE)
I---r-'-~ -,
8.00
.149 DIA. TOP X
.156 DIA. BOnOM X
.430DP.
4PL
I
L----7.50---~.1 t1 .. ::
0
NOTES: DIMENSIONS GIVEN IN INCHES.
1.10.1 Hardware
Figure 1-1
TM848 Disk Drive Mounting Configuration
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.
1.11 DISKETTE CARE, HANDLING, 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.
Ei. Put the diskette into its jacket when it is not in use.
6. Store the diskette at temperatures between 1 DoC 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-providedD.C. power at +24 volts and +5 volts is required foroperation
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. Drive 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 n~twork, which produces a pulse for each hole detected. This pulse is presented to the
user on the index pulse interface line.
1.15.2 Drive Status 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 aspindle assembly driven through adrive belt by abrushless
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
CONTROL
INDEX
LOGIC
DISK CHANGE
TWO SIDED
WRITE PROTECT
TRACK
00
IN USE
SIDE SELECT
HEAD CARRIAGE DRIVE SELECT
AND STEPPER
BAND
ASSEMBLY
SPINDLE
MOTOR CONTROL
MOTOR
CONTROL
WRITE GATE
WRITE WRITE DATA
LOGIC
CURRENT SWITCH
READ READ DATA
LOGIC
DIRECTION
STEPPER
MOTOR
CONTROL
STEP
Figure 1-2
TM848 Disk Drive Functional Block Diagram
1.15.4 Positioner Control
The head positioning system uses abipolar-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 awrite operation.
1.15.5 Data Electronics
Information can be recorded
on the diskette by using adouble-frequencycode. Figure 1-3 illustrates
the magnetization profiles
in each bit cell for the number sequence shown for FM recording.
1-9

BIT PATTERN----, BIT CELL""""
I1I1
III
II I
WRITE DATA
o
I
I
1
I
C D ic DIC CIDC ICC D
1IIII I I III I I I
III \:f.=k:1
,-,t;fl:f ~t:A1 IfI
MAGNETIZATION 1:
1II-
~ . ~
--'I I ~ I I
IIIIIIIIIII~II
M~NEnCELEMEN~ ~
I r--rTt4 II
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.
Amaximum
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.
3. 10 MA PEAKTO PEAK, TRACK0TO
TRACK42; 7.5 MAPEAK
TO PEAK,
TRACK
43 TO TRACK 77.
4. 2USEC MINIMUM
4USEC MAXIMUM
I
I
NOTES: 1. T=0= 700 MILLISECONDS AFTER DRIVE MOTOR
STARTS OR
20 MILLISECONDS AFTER LAST STEP
PULSE, WHICHEVER IS THE LATEST TIME.
2. UNSYCHRONIZED
Figure 1-4
Write Operation Timing Diagram
NOTE 2
I
~
I
~50usec""
I I
~-""""""-----""---"""~:;-"'I~
~---tl----;---+---- ........- ....... -~ ....... I ~~
II
WRITE
WAVEFORM
GENERATOR
WRITE
CURRENT
INTERNAL WRITE
BUSY
TRIM ERASE
WRITE GATE
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.
Thedrive
must be in aready condition before readingcan begin.As with the data recording operation,
this ready condition must be established by the user system. In addition to the requirements
established in this section, aperiod of 100 microseconds is necessary after atrim 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 aread preamplifier and filtered by alow-
pass
linear phase filter to remove noise (see Figure 1-5). The linear output from the filter is passed to
the differentiator,which generates awaveform whose zero crossovers correspond to the peaks of the
Read signal. This signal is then fed to the zero crossing detector and digitizer.
LINEAR OUTPUT FROM FILTER
OUTPUT FROM DIFFERENTIATOR
READ DATA INTERFACE
t
t == 0
Figure 1-5
Read Timing Diagram
Note
T=0is defined as 250 milliseconds after drive motor starts, or 20 milliseconds after a step
command, or 100 microseconds aftertermination 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 INTERFACE 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
INTERFACE CONNECTOR PIN ASSIGNMENTS
Ground
---
1
3
5
7
9
"11
'13
"15
"17
'19
:21
:23
:25
27
29
31
33
35
37
39
41
43
45
47
49
Pin Number
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
Signal
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 I ndicator (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
1-13