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 27. The values are the same for MFM and FM.
A DMA operation is selected by the ND bit. When ND is "0", the DMA mode is selected. This part does not support non-
DMA mode. In DMA mode, data transfers are signaled by the DMA request cycles.
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.
Table 27 – Drive Control Delays (ms)
HUT
SRT
2M
64
4
1M
128
8
500K 300K 250K
2M
4
3.75
..
0.5
0.25
1M
8
7.5
..
1
0.5
500K 300K 250K
0
1
..
E
F
256
16
426
26.7
..
512
32
16
15
..
26.7
25
32
30
..
..
..
..
..
..
56
60
112
120
224
240
373
400
448
480
2
3.33
1.67
4
1
2
HLT
2M
64
0.5
1
1M
128
1
500K
256
2
4
..
300K
426
3.3
250K
512
4
8
.
00
01
02
..
7F
7F
2
6.7
..
..
..
63
63.5
126
127
252
254
420
423
504
508
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 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.
PRETRK - Pre-Compensation Start Track Number. Programmable from track 0 to 255. Defaults to track 0. A "00"
selects track 0; "FF" selects track 255.
Version
The Version command checks to see if the controller is an enhanced type or the older type (765A). A value of 90 H is
returned as the result byte.
Relative Seek
The command is coded the same as for Seek, except for the MSB of the first byte and the DIR bit.
SMSC DS – LPC47M14X
Page 57
Rev. 05/02/2000
SMSC [ SMSC CORPORATION ]
