
SMSC DS – LPC47M14X 
Page 57 
Rev. 05/02/2000 
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 
.. 
56 
60 
1M
128 
8 
.. 
112 
120 
500K
256 
16 
.. 
224 
240 
300K
426 
26.7 
.. 
373 
400 
250K
512 
32 
.. 
448 
480 
2M
4 
3.75 
.. 
0.5 
0.25 
1M
8 
7.5 
.. 
1 
0.5 
500K
16 
15 
.. 
2 
1 
300K
26.7 
25 
.. 
3.33 
1.67 
250K
32 
30 
.. 
4 
2 
0 
1 
.. 
E 
F 
HLT
2M
64 
0.5 
1 
.. 
63 
63.5 
1M
128 
1 
2 
.. 
126 
127 
500K
256 
2 
4 
.. 
252 
254 
300K
426 
3.3 
6.7 
.. 
420 
423 
250K
512 
4 
8 
. 
504 
508 
00 
01 
02 
.. 
7F 
7F 
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.