..
E
F
..
56
60
..
112
120
..
224
240
..
373
400
..
448
480
..
0.5
0.25
..
1
0.5
..
2
1
..
3.33
1.67
..
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.
performed while the drive head is loaded and the
head unload delay has not expired.
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.
Configure
PRETRK
-
Pre-Compensation Start Track
The Configure command is issued to select the
Number. Programmable from track 0 to 255.
Defaults to track 0. A "00" selects track 0; "FF"
selects track 255.
special features of the FDC.
command need not be issued if the default values
of the FDC meet the system requirements.
A Configure
Configure Default Values:
EIS - No Implied Seeks
EFIFO - FIFO Disabled
POLL - Polling Enabled
FIFOTHR - FIFO Threshold Set to 1 Byte
PRETRK - Pre-Compensation Set to Track 0
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".
POLL - Disable polling of the drives. Defaults to
"0", polling enabled. When enabled, a single
interrupt is generated after a reset. No polling is
67
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