LPC47M14X datasheet(57/205 Pages) SMSC

57 / 205 page

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

500K

300K

250K

500K

300K

250K

128

112

120

256

224

240

426

26.7

373

400

512

448

480

3.75

0.5

0.25

7.5

0.5

26.7

3.33

1.67

HLT

500K

300K

250K

0.5

63.5

128

126

127

256

252

254

426

3.3

6.7

420

423

512

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.

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