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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
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