PART 2
THEORY OF OPERATION
INTRODUCTION
The
Disk
Drive
consists
of
the
mechanical and electrical
components necessary
to
record and read digital data on a
diskette.
DC
power at ±12V and +5V (provided by the
user for
the
external drives)
is
required for operation.
ORGANIZATION
Of
THE DISK
DRIVE
All
electrical subassemblies
in
the Disk Drive are constructed
with leads which terminate
in
4
or
5 pin connectors, ena-
bling the individual assemblies
to
be
removed.
The magnetic head
is
connected to the
PC
board
via
a cable
terminating
in
a 5-pin female connector and its associated
male socket which
is
located
in
close proximity
to
the read/
write data electronics.
Interface signals and power are provided
via
connectors at
the rear
of
the Drive. A detailed description
of
these signals
is
presented
in
Part 3
of
this manual.
FUNCTIONAL
BLOCK
DIAGRAM
DESCRIPTION
Figure 4
is
a functional block diagram
of
the
Disk
Drive and
should
be
referred
to
in
conjunction with the following
discussion:
The
Disk
Drive consists
of
the following functional groups:
* Index Pulse Shaper
* Write Protect Sensor
* Track
00
Sensor
* Spindle Drive Control
* Carriage Position Control
* Write/Erase Control
* Read Amplifier and Digitizer
INDEX
An
index pulse
is
provided to the user system
via
the
INDEX
PULSE
interface line. The index circuitry consists
of
an
Index LED, Index Phototransistor and a Pulse Shaping
Network.
As
the index hole
in
the disk passes the Index
LED/Phototransistor combination, light from the
LED
strikes the Index Phototransistor causing it
to
conduct. The
signal from the Index Phototransistor
is
passed
to
the Pulse
Shaping Network
whi(::h
produces a pulse for each hole
de-
tected. This pulse
is"
presented
to
the user on the INDEX
PULSE interface line.
WR
ITE PROTECT
A Write Protect signal
is
provided to the user system
via
the
WR
ITE
PROTECT interface line. The write protect circuitry
consists of a Write Protect Sensor and circuitry
to
route the
signal produced.
When
a write protected diskette
is
inserted
in
the drive, the
sensor
is
activated and the logic disables the write elect-
ronics and supplies the status signal
to
the Interface.
TRACK
00
SWITCH
The
level
on the TRACK
00
interface line
is
a function of
the position of the magnetic head assembly.
When
the head
is
positioned at Track
00
and the stepper motor
is
at the
home position, a true
level
is
generated and sent
to
the
user.
SPINDLE
DRIVE
The Spindle Drive system consists of a spindle assembly
driven
by
a
DC
motor-tachometer combination through a
drive belt.
Associated with the spindle drive motor
are
the servo elec-
tronics required for control.
The control circuitry also includes a current limiter and
an
interface control line.
When
the DRIVE
MOTOR
ENABLE
interface line
is
true, the drive motor
is
allowed
to
come up
to
speed.
When
the current through the drive motor exceeds
1.3
A,
the current limit circuitry disables the motor drive.
POSITIONER CONTROL
The Head Positioning system utilizes a four-phase stepper
motor drive which changes one phase for each track
ad-
vancement
of
the ReadlWrite carriage.
In
addition
to
the
logic
necessary for motion control, a gate
is
provided
as
an
element for inhibiting positioner motion during a write
operation.
97
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