Index Detector; Track Zero Indication; Track Accessing; Stepper Motor - Zenith Z-100 PC series Service Manual

4.7 INDEX DETECTOR
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Each time an index or sector hole is moved past the index photo detector. a pulse is formed. This pulse is present ,
on the interface as index/sector pin 8. Without a diskette in the drive. the output line will be low and the using
system must look for a transition to be a valid signal. The detector output is fed into a schmidt trigger with a level
trigger latch back to maintain pulse stability while shaping the pulse. With output enable true. this pulse will be on
the interface as a negative going pulse. See figure 4-9.
+5V
22
- -
TP7
•
-INDEX
SECTOR
-SELECT
39239-21
FIGURE 4·9. INDEX DETECTOR
4.8 TRACK ZERO INDICATION
Track 00 signal (pin 26) is provided to the using system to indicate when the read/write head is positioned on track
00. The track 00 indication is provided when the flag attached to the head carriage passes between the photo tran­
sistor and the photo detector. On track. DRIVE SELECT is ANDed with the photo detector output. These condi­
tions will cause a track 00 indication to the interface.
4.9 TRACK ACCESSING
a. Stepper Motor (Four Phase)
b. Stepper Control Logic
c. Reverse Seek
d. Forward Seek
Seeking the read/write head from one track to another is accomplished by selecting the desired direction utilizing
the DIRECTION SELECT interface line. loading the read/write head. and pulsing the STEP line .. Multiple track
accessing is accomplished by repeated pulsing of the STEP line with WRITE GATE inactive until the desired track
has been reached. Each pulse on the STEP line will cause the read/write head to move one track either in or out.
depending on the DIRECTION SELECT line.
4.9.1
Stepper Motor
The four phase stepper motor turns the head actuator cam in two step increments per track for the 455 and one
step increments for the 465. The band actuator and capstan move the heads track to track.
Two current modes are automatically enabled. The first step pulse will enable full current to the stepper motor.
Within 35 ms after that last step pulse is issued. stepper motor current is automatically decreased to approximately
50% of its full value.
4.9.2 Stepper Control
During power on reset time, the stepper control counter is reset to zero. This causes phases -8 and -A to be
energized in the stepper. Figures 4-10 and 4-11 show the stepper control logic and timing.
4·6
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