Tandon TM848-1E User manual

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TM81
FLEH,IBIJEJli,i i
PRODUCT SPEfi~~~l1ijN ~ USER'S MANUAL

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 is intended to provide the user with detailed information adequate for the efficient
installation, operation, and service of the equipment involved.
However, while every effort has 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
'anaiiii CORPORATION
20320 PRAIRIE STREET
CHATSWORTH, CALIFORNIA 91311
©COPYRIGHT 1983 TANDON CORPORATION

Section
Number
SECTION 1
Title
GENERAL DESCRIPTION
CONTENTS
Page
Number
1.1
1.2
1.3
1.4
1.5
SECTION 2
2.1
2.2
2.3
2.4
SECTION 3
Introduction. .............................................................. 1-1
Scope
Of The Document.... .. .. .. ......... .. .. .. .. . .. 1-1
Purpose Of The Drive 1-1
Major Features.... . . .. .. .. . .. . .. .. . . .. ....... . . . .. . . .. 1-1
Microprocessor Control 1-1
Write Protect 1-1
Daisy Chain Capability... . .. . .. . . .. . . . .. .. . . . . . .. 1-1
Internal Trim Erase.. . . . . .. .. .. . .... 1-2
Industry Standard Interface Compatibility. .............................. 1-2
Acti vi ty Indica tor ....................................................... 1- 2
Direct Drive, Brushless D. C. Motor. ...................................... 1-2
Com
pact Size ............................................................ 1- 2
Diskette Lever Lock Solenoid.. .. . .. . . . . .. . . .. . . . .. 1-2
Functional Description 1-2
Power On Self-Tests '" 1-3
Physical Description. ...................................................... 1-3
PRODUCT SPECIFICATIONS
Introduction. .............................................................. 2-1
Mechanical Specifications 2-1
Electrical and Operational Specifications. .................................. 2-1
Reliability Specifications. .................... .. .. ......................... 2-1
Environmental Specifications. ............................................. 2-1
OPERATION
3.1
3.2
3.3
3.4
3.5
3.6
Introduction .
Unpacking The Drive .
Pre installation Checkout .
Mounting The Drive .
Dust Cover .
Cooling .
Interface Connections .
Input Control Lines .
Output Control Lines .
Typical Interface Characteristics .
D.C.Power .
Dri ve 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 (M1, 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) .
Wri te Protect (WP and NP) .
Write Current Switch (XC and IC) .
Diagnostic Mode of Operation (DM, DL, M1, M3, M4) .
i
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

Section
Number
3.7
Figure
Number
1-1
2-1
2-2
2-3
3-1
3-2
3-3
3-4
3-5
3-6
Table
Number
2-1
2-2
2-3
3-1
3-2
3-3
3-4
Title
Diskettes .
Loading The Diskette .
Write Protect Tab .
Diskette Handling and Storage .
ILLUSTRATIONS
FIGURES
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 .
TABLES
Title
Electrical and Operational Specifica tions .
Reliability Specifications .
Environmental Specifications .
Drive Interface Lines and Pin Assignments .
D. C. Power Connector Pin Assignments .
Option Patching .
Diagnostic Mode Of Operation .
ii
Page
Number
3-14
3-14
3-14
3-17
Page
Number
1-4
2-2
2-5
2-5
3-6
3-7
3-11
3-12
3-17
3-18
Page
Number
2-3
2-6
2-6
3-3
3-8
3-9
3-15

SECTION 1
GENERAL DESCRIPTION
INTRODUCTION
This document provides required information
in order to evaluate or incorporate Tandon's
disk drive into a system.
Tandon Corporation's Model Numbers
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 per inch recording devices.
The Model TM848 series of drives are capable
of reading and wri ting 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
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.
1.2 PURPOSE OF THE DRIVE
The TM848-1E and TM848-2E drives are
rotating disk memories designed for random
access data entry, storage, and retrieval
applications. Typical applications include
1-1
intelligent terminal controllers, micro-
computers, word processing systems, data com-
munication systems, error logging, program
loading, and point-of-sale terminals.
1.3 MAJOR 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
wi th 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
in to the dri ve, the wri te electronics are
disabled.
DAISY CHAIN CAPABILITY
The drive provides the address selection and
ga ting 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.

INTERNAL TRIM ERASE
The drive provides the control signals neces-
sary for proper trim erasure of data.
INDUSTRY STANDARD INTERFACE
COMPATIBILITY
The drive is compatible with controllers that
use an industry standard interface.
ACTIVITY INDICATOR
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 indica tor in the diagnostic
mode.
DIRECT DRIVE, BRUSHLESS D. C.
MOTOR
The spindle motor is a crystal controlled,
direct drive, brushless D. C. motor for
improved motor start time, and speed
accuracy.
COMPACT SIZE
The reduced size of the drive occupies only
one-half the mounting space required for a
conventional drive.
DISKETTE LEVER LOCK SOLENOID
The diskette lever lock solenoid is controlled
by the host system.
1.4 FUNCTIONAL DESCRIPTION
The drives are fully self-contained, and
require no operator intervention during
1-2
normal operation. Each drive consists of a
direct drive, spindle system, a head positioning
system, and a read/write system.
The TM848-1E is a single-sided drive. The
TM848-2E is adouble-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 disk ejector.
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 acon-
stant speed of 360 RPM by a crystal-
controlled, direct drive, brushless D. C. motor.
The head is loaded in to con tact with the
recording medium whenever 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 of the drive, and a
Write Protect status output signal is available
to the interface. When performing a write
operation, a0.013-inch wide, nominal, data
track is recorded. Then, this track is tunnel
erased to 0.012-inch, nominal.
Data recovery electronics inel ude alow-level
read amplifier, filter, differentiator, zero
crossover detector, and digitizing circuits. No
data-clock separation is provided.
In addition, the drive is supplied with the fol-
lowing sensor systems:
1. A Track 0 sensor detects when the
Head/Carriage Assembly is positioned
over Track o.
2. The TM848-2E has two index sensors,
each consisting of an infrared L.E.D.

light source and a phototransistor, posi-
tioned to generate a signal w hen an
index hole on the diskette is detected.
The drive can determine if asingle-
sided or double-sided diskette is
installed. This ou tpu t signal is present
at the interface.
3. A Write Protect sensor disables the
write electronics when a write-enable
tab is removed from the diskette.
POWER ONSELF- TESTS
The drive conducts a power on self-test as part
of the normal power on sequence. Two of the
tests do not require a diskette to be inserted.
These tests are: the head carriage stepping in,
away from, Track 0, and the head carriage
stepping out toward Track O. 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.
3
flashes, then 3: Fails to step out to
Track 0 or Track 0
sensor is always equal
to one.
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 wi thou t a diskette in
place, or the spindle motor fails to operate, an
error message flashes on the fron t panel
L.E.D. in the following sequence:
3 flashes, then 4: No index pulse wi th
lever closed.
1-3
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
A represen ta ti ve drive is shown in Figure 1-1.
The drive can be mounted in a vertical or hori-
zon
tal plane. However, the logic circuit board
must be on the uppermost side when the drive
is mounted horizontally.
The spindle is rotated 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 horizontal slot located at the front
of the drive.
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.
The con trol electronics of the dri ve are
moun ted on a prin ted circui t board located
above the chassis. Power and interface signals
are routed through connectors plugging
directly in to the logic circuit board. Asecond
circuit board, mounted under the drive, oper-
ates the brushless D. C. spindle motor.

FIGURE 1-1
OISI{ DRIVE

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.
, a n aDnCORPORATION, CHATSWORTH, CALIFORNIA 91311
2-1
179049-001
REV.A

;0.149 DIA TOP X
0.156 DIA BOTTOM
X
0.430 DEEP
4PLCS
I
~f--------1
I
3.50
(88.9 MM)
I
8.00
(203.2 MM)
I
12.00
t (304.8 MM)
0'75~jl
(19.0 MM) .
1.60
8.550~ (40.6MM) I
I
(217.2 MM) I ..-j
~O II~OO
~~;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;~~MM)
NOTES: 1. DIMENSIONS ARE GIVEN IN INCHES. METRIC EQUIVALENTS ARE IN PARENTHESES.
2. TOLERANCE ON
ALL DIMENSIONS IS ± .020 INCH.
3. WEIGHT
IS APPROXIMATELY 5.7 POUNDS.
FIGURE 2-1
DISK DRIVE OUTLINE DRAWING
, a n aDn CORPORATION, CHATSWORTH, CALIFORNIA 91311
179049-001
REV.A
2-2

Media
TABLE 2-1
ELECTRICAL AND OPERATIONAL SPECIFICATIONS
203.20 millimeter, 8-inch IBM industry-
standard diskette
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
Ou tside Track Radius
Both Drives
TM848-2E, Side 1
Head Life
Disk Rotational Speed,
microprocessor con
trolled
Instantaneous Speed Variation (ISV)
Motor Start Time
Seek Time, Track to Track
Head Settling Time
Average Track Access Time,
including head settling time
Data Transfer Rate
6
3 x 10 passes per track
48 TPI, both drives
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
91.75 millimeters, 3.61 inches
89.64 millimeters, 3.53 inches
15,000 media contact hours
360 RPM ±1.5 percent
±1 percent
150 milliseconds, maxim urn
3milliseconds,
minimum
15 milliseconds
91 milliseconds
500,000
bits per second
, a n aDnCORPORATION, CHATSWORTH, CALIFORNIA 91311
2-3
179049-001
REV. A

TABLE 2-1 (CONTINUED)
ELECTRICAL AND OPERATIONAL SPECIFICATIONS
Flux Reversals Per Inch (FRPD,
inside track
Both Drives, Side 0
TM848-2E, Side 1
Unformatted Recording Capacity
TM848-1E
TM848-2E
D. C. Voltage and Current
Requiremen ts
+ 24 volts D. C. Power
+5 volts D. C. Power
Typical Current Requirements
For + 24 volts D. C.
Spindle Motor
Stepper Motor
Electronics
Power Dissipation
Shipment
6,536 FRPI
6,816 FRPI
0.8 megabyte per disk
1.6 megabytes per disk
+ 24 volts, ±10 percent at 700
milliamperes, typical. For surge current
requirements, see Figures 2-2 and 2-3.
+5volts, ±5 percent at 450
milliam peres, typical
170 milliamperes
400 milliam peres
130 milliamperes
20 watts, typical
When prepared for shipment by Tandon,
the drive meets the requirements of
NSTA preshipment test procedure
Project 1A.
, anaan CORPORATION,CHATSWORTH;CAUFORNIA. 91311
2-4
I
179049-001
REV.A

Configured for stepper motor enabled during motor start, 2.25 amps typical surge.
\---+--------11-----+-----1
\
2.0 I----~
\
2.5
1.5
0.5
1.0
C
U
R
R
E
N
T
I
N0
A
M
P
S
o
50 100 150
TiME iN MiLLISECONDS
200 250
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.
/
/
/
rSTEPPER MOTOR
ENABLED
\
2.5
2.0
1.5 ------- .....
\
1.0
0.5
C
U
R
R
E
N
T
I
No
\---+--------1
A
M
P
S
o
50
100 150
TIME IN MILLISECONDS
200
250
FIGURE 2-3
+24 VOLT D. C. CURRENT, CONFIGURATION 2
, a n a on CORPORATION, CHATSWORTH, CALIFORNIA 91311
179049-001
REV.A
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
Mean Time Between Failures
Mean Time To Repair
One in 10
12
bits
One in 10
6
seeks
10,000 power-on hours
30 minutes
TABLE 2-3
ENVIRONMENTAL SPECIFICATIONS
Temperature
Operating, media dependent
N onopera ting
Relative Humidity
Operating, noncondensing,
media dependent
N onopera ting, noncondensing
o0 0 0
4.4 C to 46 C,40 F to 115 F
o0 0 0
-40 C to 71 C, -40 F to 160 F
20-to-80
percent
5-to-95 percent
, a n aDnCORPORATION, CHATSWORTH, CALIFORNIA 91311
2-6
179049-001
REV.A

SECTION 3
OPERATION
INTRODUCTION
This section contains information on how to
unpack, check out, install, and operate the
TM848-1E and TM848-2E drives.
3.1 UNPACKING THE DRIVE
The dri ves are packaged in protecti ve con-
tainers to minimize the possibility of damage
during shipment. The following list is the
recommended procedure for unpacking the
drive.
1. Place the container on a flat work
surface.
2. Remove the upper half of the container.
3. Remove the drive from the lower half
of the container.
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.
3.2 PREINSTALLATION
CHECKOUT
Before applying power to the drive, the follow-
ing inspection should be conducted:
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
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
seated.
3.3 MOUNTING THE DRIVE
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 are provided 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
ei ther plane, horizon tal 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 or incor-
porate resilient members to accommodate
tolerances. In addi tion, it is recommended
that mounting schemes include no more than
two moun ting surfaces.
The drive is manufactured and tested with
some critical internal alignments that must
be maintained. Hence, it is im portan t that the
mounting hardware not introduce significant
stress on the chassis.

DUST COVER
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.
COOLING
Heat dissipation from a single drive is nor-
mally 20 watts, 68 BTU per hour, under high
load conditions. When the drive is mounted so
the components have access to a free flow of
air, normal con vection 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 boards,
and diskettes.
When forced air is used, air flow must be
directed outward from the drive. Do not
intake air through the drive or heads and
diskettes.
3.4 INTERFACE CONNECTIONS
Interface connections for the TM848-1E and
TM848-2E are made via a user-supplied, fifty-
pin, flat ribbon connector, 3M Scotchflex, Part
Number 3415, or its equivalent. This connec-
tor mates directly with the circuit 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 a26-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.
3-2
All interface signals are TTL compatible.
Logic true (low) is +0.4 volt maximum. Logic
false (high) is +2.4 volts minimum.
INPUT CONTROL LINES
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 the resistor pack removed.
The drive can terminate the following input
lines:
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
MOTOR ON CONTROL
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
(optionaD, the Motor On Control lines are
high true (see Table 3-3 located in Section 3.6).
DRIVE SELECT LINES
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
con troller.
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/

TABLE 3-1
DRIVE INTERFACE LINES AND PIN ASSIGNMENTS
Ground Pin Signal
12
Wri te Current Switch
34
Motor On Control 1
56
Motor On Control 2
78
True Ready, (Motor On Control 3, Optional)
910 Two Sided (Strappable) (TM848-2E only)
11 12
Disk Change (Strappable)
13
14 Side Select (TM848-2E only)
15 16
In Use Indicator (Strappable)
17
18 Head Load Line/Motor Con trol
19
20
Index
21 22
Ready
23
24 Motor On Control 4
25
26 Dri ve Select 1(Side Select Option, TM848- 2E only)
27
28
Drive Select 2(Side Select Option, TM848-2E only)
29
30 Drive Select 3(Side Select Option, TM848-2E only)
31
32
Drive Select 4(Side Select Option, TM848-2E only)
33
34
Direction Select (Side Select Option, TM848-2E only)
35 36
Step
37
38
Write Data
39
40 Write Gate
A'"
An
Track 0
Lt.1.
Lt~
43
44 W ri te Protect
45 46
Read Data
47 48
Alternate I/O
49 50
Alternate I/O
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 is determined 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) sta te until any operation in progress
(Step, Read/Write) is completed.
Using Side Select options 1B through 4B,
Drive Select lines may be used as Side Select
lines for the TM848-2E (see Section 3.6).
3-3
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, ini tia tes 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 of the disk if the 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 1micro-
second prior to the corresponding rising edge
of the step pulse, and remain stable 100 nano-
seconds after it.

NOTE
TM848-1E and TM848-2E
drives include amicroprocessor-
con
trolled buffered seek ca pa-
bility. The controller may issue
step pulses of one microsecond
minim urn wid th, and fifteen
microseconds minim urn spacing
between trailing edges. Internal
drive electronics issue step com-
mands at a rate of three
milliseconds.
The drive electronics ignore step pulses when
one of five conditions exists:
1. The Write Gate is true (low).
2. The Direction Select is false (high),
and the head is positioned at Track o.
3. The drive is not selected.
4.
When trying to seek beyond Track 76.
5. When the diskette lever is opened.
COMPOSITE WRITE DATA
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
com bined Wri te Da ta signal, it is recom-
mended that the repetition of the high-to-Iow
transitions, while writing all zeros, be equal to
the nominal data rate, ±0.1 percent, and the
repetition of the high-to-Iow transitions, while
wri ting all ones, be equal to twice the nominal
data rate, ±0.1 percent.
Host controllers may implement write precom-
pensa tion circuits that recognize worst case
3-4
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.
WRITE GATE
When this signal is true (low), the write
electronics are prepared for writing data and
the read electronics are disabled. This signal
turns on W ri te Current in the selected Read/
Write head. Data is written under the control
of the Composi te 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.
NOTE
Changes of state of the W ri te
Gate line should occur before
the first Write Data pulse.
INUSE
This strappable feature controls the lever lock
solenoid
when the DL option is installed.
WRITE CURRENT SWITCH
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.
SIDE SELECT
The Side Select interface line, available only
on Tandon's TM848-2E, defines which side of
atwo-sided diskette is used for reading or
writing. An open circuit, false (high) level

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 of the drive. When switch-
ing from one head to the other, a100 micro-
second
delay is required before any Read or
Write operation can be initiated.
HEAD LOAD LINE/MOTOR CONTROL
This line may be used to control the spindle
motor and/or the lever lock solenoid (see
Section 3.6).
OUTPUT CONTROL LINES
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.
INDEX
The Index signal represents the output of the
Index sensor. An Index pulse is provided 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 timing
accuracy. The Index line remains in the true
(low) state for the duration of the Index pulse,
which is nominally four milliseconds.
TRACK 0
When the drive is selected, the Track 0 in ter-
face signal indicates to the con troller 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 o. This signal is false (high)
when the selected drive's Read/Write head is
not on Track O.
3-5
WRITE PROTECT
The W ri te Protect signal is provided to indi-
ca te 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 be performed.
READ DATA
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-
si tion recorded and detected on the 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.
READY
The Ready interface signal indicates adisk-
ette has been inserted into the drive. Ready
will not return to the false state until the
lever is opened, and is not affected by Spindle
Motor Control.
When asingle-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 atwo-sided diskette is
installed, Ready is active when either side of
the diskette is selected on the TM848-2E.
TRUE READY
The True Ready interface signal indicates the
diskette is rotating at 360 RPM, and a seek
operation is complete, Le., the head has
settled. This may be used to indicate seek com-
plete when using the buffered seek operation.