Commodore Amiga A1000, Hardware Reference Manual

Page: 248 / 380

After turning on the motor, software must further wait
for one half second (500ms), or for the DSKRDY* line to
go low.
PB6 DSKSEL3* Select drive 3 (active low).
PB5 DSKSEL2* Select drive (active low).
PB4 DSKSEL1* Select drive 1 (active low).
PB3 DSKSEL0* Select drive 0 (internal drive) (active low).
PB2 DSKSIDE Specify which disk head to use. Zero indicates the
upper head. DSKSIDE must be sTable for 100
microseconds before writing. After writing, at least
1.3 milliseconds must pass before switching DSKSIDE.
PB1 DSKDIREC Specify the direction to seek the heads. Zero implies
seek towards the centre spindle. Track zero is at the
outside of the disk. This line must be set up before
the actual step pulse, with a separate write to the
register.
PB0 DSKSTEP* Step the heads of the disk. This signal must always be
used as a quick pulse (high, momentarily low, then high).
The drives used for the Amiga are guaranteed to get to
the next track within 3 milliseconds. Some drives will
support a much faster rate, others will fail. Loops
that decrement a counter to provide delay are not
accepTable. See Appendix F for a better solution.
When reversing directions, a minimum of 18 milliseconds
delay is required from the last step pulse. Settle time
for Amiga drives is specified at 15 milliseconds.
FLAG DSKINDEX* Disk index pulse ($BFDD00, bit 4). Can be used to
create a level 6 interrupt. See Appendix F for details.
- Interface Hardware 239 -