AT&T 3B2/300 Technical Reference Manual page 537

FUNCTIONAL D E S C R I P T I O N - - - - - - - - - - - - - - - - - - - - - - - - - - -
TANDON Model TM 55-4 Floppy Disk Drive
Figure 3-88 is a functional block diagram of a floppy disk drive. The floppy disk drive consists of a
spindle drive mechanism, head positioning mechanism, control logic, and read/write logic. Some of
the features are as follows.
Index Generator/Detector
An index pulse is generated once every revolution of the floppy disk to indicate the
beginning of a track to the control logic.
Write Protection Logic
When the Write Protect lead is asserted (low) the diskette is write protected by
disabling the write logic. When the Write Protect signal is high, the write logic is
enabled. A write protect tab on the diskette asserts the Write Protect signal.
Logical Drive/Side Selection
The floppy disk drive is selected by the Drive Select Lead O from the Integral
Floppy Disk Controller or CM195H Cartridge Tape Controller depending on the
application. The drive identification jumpers are set for a drive O identification for
all 382 computer floppy disk configurations. Drive Select leads 3-1 are not
connected. The side selection (0 or 1) is controlled by the Side Select lead. Side 0
is selected by a high (1) Side Select signal. Side 1 is selected by a low (0) Side
Select signal. (Head O is the lower of the two heads.)
Head Positioning Mechanism
The heads are positioned over the desired cylinder by a 4-phase stepper motor.
When the drive is selected the read/write heads are positioned to track 0. The
Track O[O] signal is asserted by the positioning logic as long as the heads are
positioned at track 0.
Disk Hub Speed Control
The drive hub is maintained at a constant speed of 300 revolutions per minute by a
servo-controlled DC motor. Motor speed stablizes at 300 revolutions per minute in
less than 250 milliseconds.
3-284 TECHNICAL REFERENCE MANUAL