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CONTROLLER
:
STEPPER CIRCUIT
1
srEP DIRECTION
SEEK COMPLETE
HEAD SELECT
READY
1
0,1,2
TRACK 0
1
STEPPER MOTOR
+
+
DRIVE
r--
SELECT
1
:.
WRITE CIRCUIT
INDEX
~
MICROPROCESSOR
IWR
CIRCUIT
(6500)
MOTOR VOLTAGE
SPINDLE SPEED
1
-
CONTROL LSI
TRACK 0
H--
1
CIRCUIT
1
SPINDLE MOTOR
7.0
MICRO-
PROCESSOR
FIGURE 25:
MPU: PC Board
20292-XXX
MPU: PC BOARD 20292-XXX
7.1
The microprocessor monitors and controls the internaI drive functions and the
host interface lines. The MPU has only three active modes: Initializing, Seek-
ing, Waiting.
As the drive spins-up, 660 revolutions are counted before the MPU assumes that
the drive is at nominal speed. The drive then initiates recalibration. If the heads
are not over Track 0, the drive will step at 3 msec./track. When both mechani-
cal Track 0 and electrical phase A are present, the heads are at true Track 0
and stepping will cease.
Within 20 msec. both SEEK COMPLETE, Track 0 and READY will go true
and the drive is then ready to accept inputs from the controller.
When in the idle mode, the MPU loops, waiting for step pulses. The MPU also
monitors its reset line (pin 39) for a Iow signal from IC4D, which causes the
MPU to reinitialize.
Upon receiving a step pulse, the MPU pauses for 500 p,sec., to allow for addi-
tional pulses, before executing the seek operation. Every incoming pulse will
reset the 500 p,sec. timer. The seek will not begin until the last pulse is received.
When seeking, the MPU counts the number of tracks to be covered and searches
the PROM for the optimum acceleration/deceleration algorithim. Steps are ac-
complished by setting IC1A to sequential phases. It provides both a current source
and sink with the motor windings. Near the end of a seek, IC 1C and 2A are
set to provide additional current to offset hysteresis.
Upon completion of a seek operation settling time is calculated, based upon
the Iength of the seek, and the interface line is activated in the specified time
periode With SEEK COMPLETE, the MPU returns to the idle mode.
Whenever a seek operation crosses the write current boundary switch at Track
128, the MPU reduces the write CUITent to eliminate pulse crowding during write
operations.
ST212 PRODUCT MANUAL/Rev. B
29
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