MPI 40 Series - Drive Select; Track Positioning; Direction Select; Step out

SELECT interface line. Only the selected drive will respond to the
controller commands for action or provide drive status to the con-
troller. In standard operation, activating DRIVE SELECT will load
the read/write heads, enable the stepper motor, enable input and
output interface lines, turn on the activity indicator and lock
the door.
In the standard drive, DRIVE SELECT 1 is enabled by jumper Bll-Cll.
DRIVE SELECT 1 will cause U37-3 (page 3, area A7) to go low, which
through jumpers L21-L22, L19-L20, and Ll8-M18 cause U29-6 (area,B6)
to go high loading the head and enabling the stepper motor (area B2)
with K9-Kl0 installed. The output status lines are enabled by a
high on U36-1 (area CS); the door is locked and the activity indi-
cator is illuminated by a low on U21-2 and 7 (area B2) which can
be traced back to a high on U20-3, and jumper J8-J9 (area BS)
respectively.
3.6.3 Track Positioning
After initializing to Track 00 with DC power on, as discussed in
paragraph 3.6.1, the read/write heads can be positioned on any
desired track by:
A. Activating the proper DRIVE SELECT line.
B. Selecting the desired direction using the DIRECTION SELECT
line.
C. Pulsing the STEP line.
Each pulse on the STEP line (Pl-36) will cause the read/write heads
on the selected drive to move one track forward or reverse, depend-
ing on the DIRECTION SELECT line (Pl-34). By repeatedly pulsing the
STEP line, consecutive tracks can be accessed. At the track zero
position the stepper phase selection flip flops (U7) (area C6) are
both reset enabling stepper motor phases one and four. The "D"
inputs to both flip flops are fed by separate gate, U26 (area C6).
These gates sample the flip flop outputs and the condition of
DIRECTION SELECT. The STEP signal clocks both flip flops as an out-
put of U31-8 (area B-6), which is enabled by WRITE GATE (Pl-40)
being false (high). Refer to figure 3-11 for timing characteris-
tics. During the write operation track positioning is inhibited.
Head movement is initiated on the trailing edge of the STEP pulse.
See Figure 3-7 for timing constraints.
3.6.3.1 Step Out
When the DIRECTION SELECT line is inactive, or false (+ 2.sv to
S.2SV), a pulse on the STEP line will cause the read/write heads
to move one track away from the center of the disk (out). The
DIRECTION SELECT and STEP lines must have the timing charac-
teristics shown in Figure 3-7.
3-18