ACT apricot - Page 209

DISK DRIVE
Direction For each valid step pulse, the head moves in
one track location towards track 69, if the
direction control line is at logic low; and one
track location towards track 0, if at logic high.
If the head is already at either track 0 or track
69
and a step pulse is issued with the direction
input set to move the head outside the normal
track range, the head is held stationary.
Active state, logic low. When active, causes the
disk to make contact with the drive head, if the
drive is selected. An indication that the head is
loaded is provided
by the activity indicator on
the front panel. If the drive is deselected, whilst
the head load signal is still active, the head
remains loaded.
Active state, logic low.
When active; enables
the drive write control circuits to receive the
write data from the disk controller; switches
current through to the read/write head; and
also enables
the tunnel erase head. Set to the
inactive high state during disk read and all head
positioning operations.
MFM encoded serial data. Changes
the polarity
of
the current flowing through the read/write
head on each negative-going transition,
providing
the following conditions are met:
1. The drive is selected.
2.
The Write Gate input is active.
3. A
write unprotected disk is inserted.
4. The drive motor is rotating at
operational speed.
5. The head has been loaded and is
stationary.