First the drive should be selected and "direction select" should be set to its correct
logic level, then "step" should be set to a logic low level. A minimum of 1µs is
necessary before the step signal may make its low-to-high transition (trailing edge of
"step") to initiate head-carriage movement. The minimum allowable time between
trailing edges of "step" is 3ms. The minimum allowable pulse width for "step" is 1µs.
Any change in "direction select" must be made at least 1µs before the trailing edge
of "step" and "direction select" logic level must be maintained 1µs after the trailing
edge of "step".
If the drive is not properly selected or a write operation is in process, the "step"
pulses from the host system will be ignored.
If "direction select" is at a logic low level and the head carriage is at the innermost
track (Track 79), step pulses issued by the host system would attempt to move the
head carriage assembly until it is stopped by the mechanical safety stop installed on
the drive.
However, driving the head-carriage assembly of the drive into the safety stops is not
recommended. The host system controller should know the position of the head-
carriage assembly at all times by reading the sector or track ID address field. In the
event that the controller loses track of the head-carriage assembly's location, it is
recommended that "direction select" be set to a logic high level and several step
pulses be issued. After every step pulse issued to the drive, "Track 00" signal's level
should be checked whether it has returned to a true state (logic low). In order to
assure proper positioning of the read/write heads after power-on, the head-carriage
assembly will step out to Track 00 during the power-on procedure.
Thus, the read/write head assembly of the drive is automatically positioned to
Track 00 after
power is switched on.
2.2.5
Write data (J1 pin #22)
This interface line provides the data to be written on the diskette in the appropriate
sector. Each transition from a high logic level to a low logic level on this line causes
the write current through the head to be reversed. This line is enabled by "write
gate" being active. "Write data" must be inactive during a read operation. If the
drive is not properly selected, a write-protected diskette is installed, a seek operation
is not completed, or the drive has no diskette installed, the write data will be ignored.
2.2.6
Write gate (J1 pin #24)
The active state (logic low) of this line enables "write data" to be written on the
diskette. The inactive state (logic high) enables the read data logic and seek
operations.
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Leaflet No. 9419 26/4/97 6:09 pm Page 11
