Tandon TM848-1E Installation instructions

TN84%5 i 48-2E
FLEXISLK 9I8g j%)RIVES
MJ' 4 il [
PRODUCTSPE
/IFICATION AND USER'SMANUAL

NOTICE
This document, and the information contained herein, is copyright by Tandon Corporation and
may not be duplicated or reproduced, in whole or in part, without the prior written approval of
Tandon Corporation.
This document isintended to provide the user with detailed information adequate for the efficient
installation, operation, and service of the equipment involved.
However, while every efforthas been made to keep the information contained herein current and
accurate as of the date of publication, no guarantee is given or implied as to its accuracy.

TM848-1E, TM848-2E
THINLINE™ FLEXIBLE DISK DRIVE
48 TRACKS PER INCH
PRODUCT SPECIFICATION AND USER'S MANUAL
lcllld D I 1CORPORATION
CHATSWORTH, CALIFORNIA 91311
20320 PRAIRIE STREET
o COPYRIGHT 1983 TANDON CORPORATION

CONTENTS
Section
Number
SECTION 1 G E N E R A L DESCRIPTION
Page
Number
Title
1.1
1.2
1.3
1.4
Introduction
Scope Of The Document... . . . . . . . . . . . . . . . . . . . .
Purpose Of The Drive
Major Features
Microprocessor Control
Write Protect .
Daisy Chain Capability
Internal Trim Erase
Industry Standard Interface Compatibility.
Activity Indicator .
Direct Drive, Brushless D. C. Motor
Compact Size
Diskette Lever Lock Solenoid
Functional Description
Power On Self- Tests
Physical Description
1-1
1-1
1-1
1-1
1-1
1-1
1-1
1-2
1-2
1-2
1-2
1-2
1-2
1-2
1-3
1-3
1.5
SECTION 2 PRO DUCT SPECIFICATIONS
Introduction .
Mechanical Specifications .
Electrical and Operational Specifications
Reliability Specifications
Environmental Specifications .
2-1
2-1
2-1
2-1
2-1
3.4
3.1
3.2
3.3
2.1
2.2
2.3
2.4
SECTION 3 OPERATION
Introduction
Unpacking The Drive
Preinstallation Checkout
Mounting The Drive .
Dust Cover .
Cooling .
Interface Connections
Input Control Lines
Output Control Lines ..
Typical Interface Characteristics
D. C. Power .
Drive Address and Option Strapping
Drive Select (DS1 — DS4)
Head Select Options (Sl — S3 and 1B — 4B) .
Stepper Motor Power (PS, PS*, DS, HL) .
Spindle Motor Control Options (Ml, M3, M4, MOL, MOH, MC1 — MC4)
Ready and True Ready (R and TR)
Lever Lock Options (D, DL, LL, NL)
Disk Change (DC) .
Two-Sided Diskette Installed (2S),
Write Protect (WP and NP) .
Write Current Switch (XC and IC)
Diagnostic Mode of Operation (DM, DL, Ml, M3, M4) .
3-1
3-1
3-1
3-1
3-2
3-2
3-2
3-2
3-5
3-6
3-6
3-8
3-8
3-8
3-10
3-10
3-13
3-13
3-13
3-13
3-13
3-14
3-14
3.5
3.6

Section
Number Page NumberTitle
3-14
3-14
3-14
3-17
Diskettes
Loading The Diskette
Write Protect Yab .
Diskette Handling and Storage
ILLUSTRATIONS
FIGURES
Figure
Number Page Number
n r
1-1
2-1
2-2
4-o
Title
Disk Drive
Disk Drive Outline Drawing
+24 Volt D. C. Current, Configuration 1
+ 24 Volt D. C. Current, Configuration 2
Electrical Interface Characteristics .
Control and Data Timing Requirements
LSI Circuit Board Assembly .
Non-LSI Circuit Board Assembly .
Recording Media
Diskette Care and Handling .
1-4
2-2
2-5
2-5
3-6
3-7
3-11
3-12
3-17
3-18
3-1
3-2
3-3
3-4
3-5
3-6
TABLES
Table
Number Page
Number
2-1
2-2
2-3
3-1
3-2
3-3
3-4
Title
Electrical and Operational Specifications .
Reliability Specifications .
Environmental Specifications
Drive Interface Lines and Pin Assignments
D. C. Power Connector Pin Assignments ..
Option Patching
Diagnostic Mode Of Operation
2-3
2-6
2-6
3-3
3-8
3-9
3-15
11

SECTION 1
GENERAL DESCRIPTION
INTROOU CTION intelligent t erm ina l con tr ollers, m icro-
computers, word processing systems, datacom-
munication systems, error logging, program
loading, and point-of-sale terminals.
This document provides required information
in order to evaluate or incorporate Tandon's
disk driveinto a system.
Tandon Corporation's Model Num b ers
TM848-1E and TM848-2E, eight-inch flexible
drives are full-feature, microprocessor-
controlled drives. They may be installed in
one-half the space normally required for an
eight-inch drive.They are compact data stor-
age devices that use an IBM-formatted, indus-
try standard, eight-inch diskette. Both drives
are 48 tracks perinch recording devices.
The Model TM848 series ofdrives are capable
of reading an d writ ing in single-density
format on a diskette, using a proprietary
read/write head patented by Tandon. In
addition, both drives have a double density
capability when Modified Frequency Modula-
tion (MFM) or other appropriate recording
techniques are used. The encoding and decod-
ing of the data is done by the user's controller.
The Model TM848-1E drive uses one side of
the diskette for data storage.The Model
TM848-2E drive doubles data storage capabili-
ties by using both sides of the diskette.
1.1 SCOPE OF THE DOCUMENT
1.3 MA JOR FEATURES
MICROPROCESSOR CONTROL
The TM848-1E and TM848-2E drives feature
an onboard microprocessor. This microproces-
sor provides six major features:
1. Buffered seek capabilities..
2. Improved head positioning accuracy
with reduced hysteresis.
3. Write current switching for optimal
data recording quality.
4. True Ready signal.
5. Internal diagnostics (strappable).
6. Power On Self- Tests.
WRITE PROTECT
When a write protected diskette is inserted
into the dr ive, the write electronics are
disabled.
This document contains a description of the
major features, physical and functional speci-
fications, mounting and power requirements,
the interface, and typical timing characteris-
tics of the TM848-1E and TM848-2E drives. DAISY CHAIN CAPABILITY
1.2 PURPOSE OF THE DRIVE The drive provides the address selection and
gating functions necessary to daisy chain a
maximum of four units at the user's option.
The last drive on the daisy chain terminates
the interface. The terminations are accom-
plished by a resistor array plugged into a DIP
socket.
The TM848-1E and TM 848-2E drives are
rotating disk memories designed for random
access data entry, storage, and retrieval
applications. Typical applications include
1-1

INTERNAL TRIM ERASE
accuracy.
COMPACT SIZE
ACTIVITY INDICATOR
DIRECT DRIVE, BRUSHLESS D. C.
MOTOR
INDUSTRY STANDARD INTERFACE
CO MPATI BILITY
DISKETTE LEVER LOCK SOLENOID
The reduced size of the drive occupies only
one-half the mounting space required for a
conventional drive.
The spindle motor is a crystal controlled,
direct drive, brushless D. C. motor for
improved motor start time, and speed
The drive provides the control signals neces-
sary forproper trim erasure ofdata.
The drive is compatible with controllers that
use an industry standard interface.
An activity indicator, located on the front
panel, is automatically illuminated when the
drive is selected. This front panel L.E.D. is
also used as an indicator in the diagnostic
mode.
normal operation. Each drive consists of a
direct drive, spindle system, a head positioning
system, and aread/write system.
The TM848-1E is a single-sided drive. The
TM848-2E is a double-sided drive. The only
difference between the two drives is the
number of heads.The circuit board is identical
for both models.
When the diskette lever is opened, access is
provided for the insertion of a diskette. The
diskette's jacket is accurately positioned by
plastic guide rails. Its location is ensured by
the back stop and diskejector.
Closing the diskette lever activates the
cone/clamp system, resulting in accurate
centering and clamping of the diskette to the
drive hub. The drive hub is driven at a con-
stant speed of 360 RPM by a cryst al-
controlled, direct drive, brushless D. C. motor.
The head is loaded into contact with the
recording medium wh enever the diskette
lever is latched.
The heads are positioned over the desired
track by means of a stepper motor/band
assembly and its associated electronics. This
positioner uses 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 dis-
ables the write electronics ofthe drive, and a
Write Protect status output signal is available
to the interface. When performing a wr ite
operation, a 0.013-inch wide, nominal, data
track is recorded. Then, this track is tunnel
erased to 0.012-inch, nominal.
Data recovery electronics include a low-level
read amplifier, filter, differentiator, zero
crossover detector, and digitizing circuits. No
data-clock separation isprovided.
In addition, the drive is supplied with the fol-
lowing sensor systems:
The diskette lever lock solenoid is controlled
by the host system.
1.4 FUNCTIONAL DESCRIPTION 1. A Track 0 sensor detects when the
Head/Carriage Assembly is positioned
over Track 0.
2. The TM848-2E has two index sensors,
each consisting of an infrared L.E.D.
The drives are fully self-contained, and
require no operator i nt e rvention during
1-2

light source and a phototransistor, posi-
tioned to generate a signal when an
index hole on the diskette isdetected.
The drive can determine if a single-
sided or double-sided diskette is
installed. This output signal is present
at the interface.
Opening and closing the diskette lever is
required to repeat a test that has failed. The
diskette lever must be left open to complete
an error cycle.
1.5 PHYSICAL DESCRIPTION
3. A Write Protect sensor disables the
write electronics when a write-enable
tab isremoved from the diskette.
POWER ON SELF- TESTS A representative drive is shown in Figure 1-1.
The drive can be mounted in a vertical or hori-
zontal plane. However, thelogic circuit board
must be on the uppermost side when the drive
is mounted horizontally.
The drive conducts apower on self-test as part
of the normal power on sequence. Two of the
tests do not require a diskette to be inserted.
These testsare: the head carriage stepping in,
away from, Track 0, and the head carriage
stepping out toward Track 0. Failure of either
of these tests is indicated on the front panel
L.E.D. by the following flashing sequence:
3 flashes, then 2: Fails to step in from
Track 0 or Track 0
sensor is always equal
to zero.
The spindle isrotated by a direct drive, brush-
less D. C. motor with an integral tachometer.
The crystal-controlled servo circuit and
tachometer control the speed of the spindle.
Operator access for diskette loading is pro-
vided via a horizontalslotlocated at the front
of the drive.
3 flashes, then 3: Fails to st ep out t o
Track 0 or Track 0
sensor is always equal
to one.
The read/write double-head assembly is posi-
tioned by a split band positioner mounted to a
microprocessor-controlled stepper motor. The
read/write heads are glass-bonded, ferrite/
ceramic structures with a life expectancy of
15,000 operating hours.
A third test monitors the index sensors when-
ever the diskette lever is closed, and must
have a diskette inserted into the drive.If the
diskette lever is closed without a diskette in
place, orthe spindle motor failsto operate, an
error message flashes on the front panel
L.E.D. in the following sequence:
3 flashes, then 4: No index pulse with
The control electronics of the drive are
mounted on a printed circuit board located
above the chassis. Power and interface signals
are routed t hr o ugh co nnectors plugging
directly into the logic circuit board. A second
circuit board, mounted under the drive,oper-
ates the brushless D. C. spindle motor.lever closed.
1-3

~>GURp y.y
OISK Qp]yp

SECTION 2
PRODUCT SPECIFICATIONS
INTRODUCTION
This section contains the mechanical, electrical, reliability, and environmental specifications for the
TM848-1E and TM848-2E drives.
2.1 MECHANICAL SPECIFICATIONS
Figure 2-1 contains the physical dimensions of the drive.
2.2 ELECTRICAL AND OPERATIONAL SPECIFICATIONS
The electrical and operational specifications are located in Table 2-1.
2.3 RELIABILITY SPECIFICATIONS
The reliability specifications are located in Table 2-2.
2.4 ENVIRONMENTAL SPECIFICATIONS
The environmental specifications are located in Table 2-3.
1 7 9049-001
REY. A
CRVI C I E3 f l COR ORA ON,CH TSWORTII,CAL O • IA 9 1
2-1

6-32 THD
THRU 4 PLCS
(2 EACH SIDE) Q5)
Go O0
1 2.00
' (304.8 MM) / 0.149 DIA TOP X
0.156 DIA BOTTOM
X 0.430 DEEP
4 PLCS
8.00
(203.2 MM)
o o o o
o) • Oo
3.50
(88.9 MM)
0 o p
L~o/1.20
(30.5 MM)
0.75~ '
(19.0 MM)
1.60
(40.6 MM)
(25.4 MM)
7. 50
(190.5 MM)
1.650
(41.5 MM)
0.52
(13.2 MM)
8.550
(217.2 MM) 2.025
(51.4 MM)
2.300
(58.4 MM)
NOTES: 1. DIMENSIONS ARE GIVEN IN INCHES. METRIC EQUIVALENTS ARE IN PARENTHESES.
2. TOLERANCE ON ALL DIMENSIONS ISH-.020 INCH.
3. WEIGHT IS APPROXIMATELY 5.7 POUNDS.
FIGURE 2-1
DISK DRIVE OUTLINE DRAWING
1 79049-001
REV. A
mn d n n DDRPDRATIDN, DHATswDR H, DALIPDRNIA 31311
2-2

TABLE 2-1
ELECTRICAL AND OP ER AT IONAL SPECIF I CATIONS
Media
6
203.20 millimeter, 8-inch IBM industry
standard diskette
3 x 10 passes per track
48 TPI, both drives
Media Life (for reference only)
Tracks Per Inch
Tracks Per Drive
TM848-1E
TM848-2E
Track Spacing
Inside Track Radius
Both Drives, Side 0
TM848-2E, Side 1
Outside Track Radius
77 tracks per drive
154 tracks per drive, 77 per side
0.529 millimeter, 20.8 milinches
51.50 millimeters, 2.03 inches
49.42 millimeters, 1.95 inches
Both Drives
TM848-2E, Side 1
91.75 millimeters, 3.61 inches
89.64 millimeters, 3.53 inches
15,000 media contact hours
Head Life
Disk Rotational Speed,
microprocessorcontrolled
Instantaneous Speed Variation (ISVl
Motor Start Time
Seek Time, Track to Track
Head Settling Time
Average Track Access Time
including head settling time
Data Transfer Rate
360 RPM ~ 1.5 percent
1 percent
150 milliseconds, maximum
3 milliseconds, minimum
15 milliseconds
91 milliseconds
500,000 bits per second
1 79049-001
REV. A
an d n n DDRPDRATIDN, DHATswDRTH,DALIFDR•IA91311

TABLE 2-1 (CONTINUED)
ELECTRICAL AND OP ERATIONAL SPECIFICATIONS
Flux Reversals Per Inch (FRPI),
inside track
Both Drives, Side 0
TM848-2E, Side 1
Unformatted Recording Capacity
6,536 FRPI
6,816 FRPI
TM848-1E 0.8 megabyte per disk
1.6 megabytes per diskTM848-2E
D. C. Voltage and Current
Requirements
+ 24 volts D. C. Power + 24 volts, ~ 10 percent at 700
milliamperes, typical. For surge current
requirements, see Figures 2-2 and 2-3.
+5 volts,~ 5 percent at 450
milliamperes, typical
+ 5 volts D. C. Power
Typical Current Requirements
For +24 volts D. C.
Spindle Motor
Stepper Motor
Electronics
Power Dissipation
Shipment
170 milliamperes
400 milliamperes
130 milliamperes
20 watts, typical
When prepared forshipment by Tandon,
the drive meets the requirements of
NSTA preshipment test procedure
Project 1A.
179049-001
REV. A
KRV I d C ln OO RPO R ATIO • .OHATSTIIORT• CALIFORNIA R 3
2-4

Configured for stepper motor enabled during motor start, 2.25 amps typical surge.
C 2 5
U
R
R
E1.5
1.O
T0.5
N o
I
50 100 150
TiME IN MiLLISECONDS
200 250
Ap
S
FIGURE 2-2
+24 VOLT D. C.CURRENT, CONFIGURATION 1
Configured for stepper motor disabled until motor comes up to speed, 1.8 amps typical surge.
STEPPER MOTOR
ENABLED
C2.5
U
R2.0
1.5
E
N10
T0.5
I
N
50 100
A150
TIME IN MILLISECONDS
200 250
Mp
S
FIGURE 2-3
+24 VOLT D. C.CURRENT, CONFIGURATION 2
1 79049-001
REY. A
an d a n cDRPDRATIDN,c •ATswDRT•,cALIFDR•IA91311
2-5

TABLE 2-2
RELIABILITY SPECIFICATIONS
Error Rates, maximum, exclusive
of external sources, e.g.:
electronics, defective and
contaminated diskettes
Soft Errors (Recoverable)
Hard Errors (Nonrecoverable)
Seek Errors 6
One in 10 bits
One in 10 bits
One in 10 seeks
10,000 power-on hours
30 minutes
Mean Time Between Failures
Mean Time To Repair
TABLE 2-3
ENVIRONMENTAL SPECIFICATIONS
Temperature
4.4 C to46 C,40 F to 115 F
— 40 C to 71 C, — 40 F to 160 F
Operating, media dependent
Nonoperating
Relative Humidity
Operating, noncondensing,
media dependent
Nonoperating, noncondensing
20-to-80 percent
5-to-95 percent
1 79049-001
REV. A
CR n d E3 & CORP ORATION, CHATSWORTH. CALIFORNIA 91311
2-6

SECTION 3
OPERATION
INTRODUCTION 3. Remove the cardboard shipping insert,
and retain for future shipment.
4. Ensure that the front panel is secure.
5. Ensure that the circuit board is secure.
6. Ensure that the connectors are firmly
This section contains information on how to
unpack, check out, install, and operate the
TM848-1E and TM848-2E drives.
seated.
3.1 UNPACKING THE DRIVE
3.3 MOUNTING THE DRIVEThe drives are packaged in protective con-
tainers to minimize the possibility of damage
during shipment. The following list is the
recommended procedure for unpacking the
drive.
CHECKOUT
3.2 PREINSTALLATION
Before applying power tothe drive,the follow-
ing inspection should be conducted:
4. Check the contents of the container
against the packing slip.
5. Investigate the contents of the con-
tainer for possible damage.
6. Notify the carrier immediately if any
damage is found.
surface.
2. Remove the upper half of the container.
3. Remove the drive from the lower half
of the container.
1. Place the container on a fla t work
The drive has been designed so it may be
mounted in any plane, i.e.: upright, horizontal,
or vertical. When mounted horizontally, the
Logic circuit board side of the chassis must be
the top side.
Eight holes areprovided for mounting: two on
each side and four on the bottom of the hous-
ing (see Figure 2-1). The two mounting holes
on each side are tapped for 8-32 screws. The
four mounting holes on the bottom require
8-32 thread forming screws. When installed in
either plane, horizontal or vertical, only two
mounting screws are required to securely hold
the drive in place.
Optional straps are available to permit two
drives to be attached together for installation
in standard width drive openings.
Any mounting scheme in which the drive is
part of the structural integrity of the enclo-
sure is not permitted, Mounting schemes
should allow for adjustable brackets orincor-
porate resilient members to accommodate
tolerances. In addition, it is recommended
that mounting schemes include no more than
two mounting surfaces.
The drive is manufactured and tested with
some critical internal alignments that must
be maintained. Hence, it is important that the
mounting hardware not introduce significant
stress on the chassis.
1. Check to ensure that the diskette lever
opens and closes.
2. When the lever is moved to an open
position,the head arm raises.
3-1

DUST COVER All interface signals are TTL compatible.
Logic true (low) is +0.4 volt maximum. Logic
false (high) is +2.4 volts minimum.
The design of an enclosure should incorporate
a means to prevent contamination from loose
items, e.g., dust, lint, and paper chad since the
drive does not have a dust cover. INPUT CONTROL LINES
COOLING These input lines are individually terminated
through a 150 ohm resistor pack installed in
the dip socket located at integrated circuit
location RP5 (or RP1 in the Large Scale Inte-
gration version). In a single-drive system, this
resistor pack should be installed to provide
the proper terminations. In a multiple-drive
system, only the last drive on the interface is
to be terminated. All other drives on the inter-
face must have theresistor pack removed.
The drive can terminate the following input
lines:
Heat dissipation from a single drive is nor-
mally 20 watts, 68 BTU per hour, under high
load conditions. When the drive ismounted so
the components have access to afree flow of
air, normal convection cooling allows opera-
tion within 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, printed circuit hoards,
and diskettes.
When forced air is used, air flow must be
directed outward from the drive. Do not
intake air through the drive nr heads and
diskettes.
1. Direction
2. Step
3. Write Data
4. Write Gate
5. In Use
6. Side Select (TM848-2E only)
7. Write Current Switch
8. Head Load
3.4 INTERFACE CONNECTIONS MOTOR ON CONTROL
Interface connections for the TM848-1E and
TM848-2E are made via a user-supplied, fifty-
pin, flatribbon connector, 3M Scotchflex, Part
Number 3415, or its equivalent. This connec-
tor mates directly with the ci rcuit board
connector at the rear of the drive.
The interface description of the connectors,
and the location of each one, is contained in
this section. Interface lines are located in
Table 3-1. D. C. power connector pin assign-
ments are located in Table 3-2, Section 3.5 of
this manual.
The signal wire harness should be of the flat
ribbon or twisted pair type, have a maximum
length of ten feet,and have a 26-to-28 gauge
conductor compatible with the connector to be
used. It is recommended that the interface
cable have a characteristic impedance of 100
ohms.
DRIVE SELECT LINES
The Motor On Control lines are used to control
the spindle motor. With the MOL jumper in
(factory installed), the Motor On Control lines
are low true. With the MOH jumper installed
(optional), the Motor On Control lines are
high true (see Table 3-3 located in Section 3.6).
The Drive Select lines provide a means of
selecting and deselecting a drive. These four
lines, DS1 through DS4, allow independent
selection of up to four drives attached to the
controller.
When the signal logic level is true (low), the
drive electronics are activated, and the drive
is conditioned to respond to Step or to Read/
3-2

TABLE 3-1
DRIVE INTERFACE LINES AND PIN ASSIGNME NT S
Ground Pin Signal
1
l 1
43
45
47
49
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
357
l A
'+8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
68
2
4Write Current Switch Motor On Control 1
Motor On Control 2
True Ready, (Motor On Control 3, Optional)
Two Sided (Strappable) (TM848-2E only)
Disk Change (Strappable)
Side Select (TM848-2E only)
In Use Indicator (Strappable)
Head Load Line/Motor Control
Index
Ready
Motor On Control 4
Drive Select 1 (Side Select Option, TM848-2E only)
Drive Select 2 (Side Select Option, TM848-2E only)
Drive Select 3 (Side Select Option, TM848-2E only)
Drive Select 4 (Side Select Option, TM848-2E only)
Direction Select (Side Select Option, TM848-2E only)
Step
Write Data
Write Gate
Track v
Write Protect
Read Data
Alternate I/O
Alternate I/O
44
46
48
50
DIRECTION SELECT AND STEP LINES
(TWO LINES)
When the drive is selected, a true (low) pulse
on the Step line, with a time duration greater
than one microsecond, initiates the access
motion. The direction of motion is determined
by the logic state of the Direction Select line
when a step pulse is issued. The motion is
toward the center ofthe disk ifthe Direction
Select line is in the true (low) state. The direc-
tion of motion is away from the center of the
disk if the Direction Select line is in the false
(high) state.
To ensure proper positioning, the Direction
Select line should be stable at least 1 micro-
second. priorto the corresponding rising edge
of the step pulse, and remain stable 100 nano-
seconds afterit.
Write commands. When the signal logic level
is false (high), the input control lines and the
output status lines are disabled,
The Drive Select address isdetermined by a
select shunt on the circuit board. Drive Select
lines 1 through 4 provide a means of daisy
chaining a maximum of four drives to acon-
troller. Only one can be true (low) at a time.
An undefined operation might result if two or
more drives are assigned the same address or
if two or more Drive Select lines are in the
true (low) state simultaneously. A Drive
Select line must remain stable in the true
(low) state until any operation in progress
(Step, Read/Write) is completed.
Using Side Select options 18 t h rough 48,
Drive Select lines may be used as Side Select
lines for the TM848-2E (see Section 3.6).
3-3

NOTE patterns and adjust the Write Data wave-
form. Although a value cannot be specified for
write precompensation, Tandon suggests a
value of 125 nanoseconds for systems using
MFM double density recording format.
TM848-1E and T M 848-2E
drives include a microprocessor-
controlled buffered seek capa-
bility. The controller may issue
step pulses of one microsecond
minimum width, and fift een
microseconds minimum spacing
between trailing edges. Internal
drive electronics issue step com-
mands at a rate of three
milliseconds.
WRITE GATE
The drive electronics ignore step pulses when
one of five conditions exists:
When this signal is true (low), the write
electronics are prepared for writing data and
the read electronics are disabled. This signal
turns on Write Current in the selected Read/
Write head. Data is written under the control
of the Composite Write Data and Side Select
input lines. When the Write Gate line is false
(high), all write electronics are disabled.
When a write protected diskette is installed in
a drive, the write electronics are disabled, irre-
spective of the state of the Write Gate or Side
Select lines. With the NP jumper installed, a
diskette cannot be write protected.
1. The Write Gate is true (low).
2. The Direction Select is false (high),
and the head is positioned at Track 0.
3. The drive isnot selected.
4. When trying toseek beyond Track 76.
5. When the diskette lever is opened. NOTE
Changes of state of the Write
Gate line should occur before
the first Write Data pulse.COMPOSITE WRITE DATA
IN USE
When the drive is selected, this interface line
provides the bit serial Composite Write Data
pulses that control the switching of the Write
Current in the selected head. The write elec-
tronics must be conditioned for writing by the
Write Enable line.
For each high-to-low transition on the Compos-
ite Write Data line, a flux change is produced
at the write head gap. This causes a flux
change to be recorded on the media.
When a double-frequency type encoding tech-
nique is used in which data and clock form the
combined Write Data signal, it is recom-
mended that the repetition of the high-to-low
transitions, while writing all zeros, be equal to
the nominal data rate, ~0.1 percent, and the
repetition of the high-to-low transitions, while
writing all ones, be equal to twice the nominal
data rate, ~ 0.1 percent.
Host controllers may implement write precom-
pensation circuits that recognize worst case
SIDE SELECT
WRITE CURRENT SWITCH
This strappable feature controls the lever lock
solenoid when the DL option is installed.
Normally, Write Current switching is accom-
plished by the host controller. A true (low)
level on this line reduces the Write Current.
Using option IC, the drive automatically
reduces Write Current at Track 43.
The Side Select interface line, available only
on Tandon's TM848-2E, defines which side of
a two-sided diskette is used for reading or
writing. An open circuit, false (high) level
3-4

WRITE P ROTECT
selects the Read/Write head on side zero,the
lower head of the drive. A true (low) level on
this line selects the Read/Write head on side
one, the upper head ofthe drive. When switch-
ing from one head to the other, a 100 micro-
second delay is required before any Read or
Write operation can be initiated.
The Write Protect signal is provided to indi-
cate to the user that a write protected diskette
is installed. This signal is true (low) when the
diskette's Write Protect notch is uncovered.
When the Write Protect signal is false (high),
the write electronics are enabled, and write
operations can beperformed.
HEAD LOAD LINE/MOTOR CONTROL
READ DATAThis line may be used to control the spindle
motor and/or the lever lock solenoid (see
Section 3.6).
OUTPUT CONTROL LINES
The Read Data line transmits data to the con-
troller when the drive is selected and not
writing. It provides a pulse for each flux tran-
sition recorded and detected onthe diskette by
the drive electronics. Normally, this signal is
false (high). It becomes true (low) for the
active state.The Read Data output line goes
true (low) for a duration of 200 nanoseconds,
~ 50 nanoseconds, for each change recorded
on the diskette.
There are eight output lines, five of which are
standard and three of which are strappable
features. The standard output signals are:
Index/Sector, Track 0, Write Protect, Read
Data, and Ready. The strappable output sig-
nals are Disk Change, Two-Sided, and True
Ready.
READY
INDEX
The Ready interface signal indicates a disk-
ette has been inserted into the drive. Ready
will not return to the false state until the
lever isopened, and is not affected by Spindle
Motor Control.
When a single-sided diskette is installed,
Ready is active (low) if side zero is selected.
Ready is false (high) if side one is selected on
the TM848-1E. When a two-sided diskette is
installed, Ready is active when either side of
the disketteisselected on the TM848-2E.
The Index signal represents the output of the
Index sensor. An Index pulse isprovided once
every revolution, 166.67 milliseconds nominal,
to indicate the beginning of a track to the
controller. The leading edge of this signal
must always be used to ensure tim ing
accuracy. The Index line remains in the true
(low) state for the duration of the Index pulse,
which is nominally four milliseconds.
TRACK 0
TRUE READY
When the drive is selected, the Track 0 inter-
face signal indicates to the controller that the
Read/Write head is positioned on Track 0, the
outermost track. This signal remains true
(low) until the Read/Write head is moved
away from Track 0. This signal is false (high)
when the selected drive's Read/Write head is
not on Track 0.
The True Ready interface signal indicates the
diskette is rotating at 360 RPM and a seek
operation is complete, i.e.,the head has
settled. This may be used to indicate seek com-
plete when using the buffered seek operation.
3-5