The values change with the data rate speed selection
and are documented in Table 30. The
values are the same for MFM and FM.
Table 28 - 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
..
64
0.5
1
128
1
2
256
2
4
426
3.3
6.7
..
512
4
8
..
..
..
.
7F
7F
63
63.5
126
127
252
254
420
423
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 signaled by the FDRQ
pin. Non-DMA mode uses the RQM bit and the FINT pin
to signal data transfers.
EIS - Enable Implied Seek. When set to "1", the FDC will
perform a Seek operation before executing a read or write
command. Defaults to no implied seek.
EFIFO - A "1" disables the FIFO (default). This means
data transfers are asked for on a byte-by-byte basis.
Defaults to "1", FIFO disabled. The threshold defaults to
"1".
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.
POLL - Disable polling of the drives. Defaults to "0",
polling enabled. When enabled, a single interrupt is
generated after a reset. No polling is performed while the
drive head is loaded and the head unload delay has not
expired.
Configure Default Values:
FIFOTHR - The FIFO threshold in the execution phase of
read or write commands. This is programmable from 1 to
16 bytes. Defaults to one byte. A "00" selects one byte;
"0F" selects 16 bytes.
EIS - No Implied Seeks
EFIFO - FIFO Disabled
POLL - Polling Enabled
FIFOTHR - FIFO Threshold Set to 1 Byte
PRETRK - Pre-Compensation Set to Track 0
65
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