
62
Sense Drive Status
Sense
Drive
Status
obtains
drive
status
information.
It has not execution phase and
goes directly to the result phase from the
command phase.
Status Register 3 contains
the drive status information.
Specify
The Specify command sets the initial values for
each of the three internal times.
The HUT
(Head Unload Time) defines the time from the
end of the execution phase of one of the
read/write commands to the head unload state.
The SRT (Step Rate Time) defines the time
interval between adjacent step pulses. Note that
the spacing between the first and second step
pulses may be shorter than the remaining step
pulses. The HLT (Head Load Time) defines the
time between when the Head Load signal goes
high and the read/write operation starts.
The
values
change
with
the
data
rate speed
selection and are documented in Table 29. The
values are the same for MFM and FM.
Table 29 - Drive Control Delays (ms)
HUT
SRT
2M
1M
500K
300K
250K
2M
1M
500K
300K
250K
0
1
..
E
F
64
4
..
56
60
128
8
..
112
120
256
16
..
224
240
426
26.7
..
373
400
512
32
..
448
480
4
3.75
..
0.5
0.25
8
7.5
..
1
0.5
16
15
..
2
1
26.7
25
..
3.33
1.67
32
30
..
4
2
HLT
2M
1M
500K
300K
250K
00
01
02
..
7F
64
0.5
1
..
63
63.5
128
1
2
..
126
127
256
2
4
..
252
254
426
3.3
6.7
..
420
423
512
4
8
.
504
508
The choice of DMA or non-DMA operations is
made by the ND bit. When this bit is "1", the
non-DMA mode is selected, and when ND is "0",
the DMA mode is selected. In DMA mode, data
transfers are signalled by the FDRQ pin. Non-
DMA mode uses the RQM bit and the FINT pin
to signal data transfers.
Configure
The Configure command is issued to select the
special features of the FDC.
A Configure
command need not be issued if the default
values
of
the
FDC
meet
the
system
requirements.