LPC47M14X datasheet(41/205 Pages) SMSC

41 / 205 page

SMSC DS – LPC47M14X

Page 41

Rev. 03/19/2001

RQM and DIO must both equal "1" before the result bytes may be read. After all the result bytes have been read, the

RQM and DIO bits switch to "1" and "0" respectively, and the CB bit is cleared, indicating that the FDC is ready to accept

the next command.

Command Set/Descriptions

Commands can be written whenever the FDC is in the command phase. Each command has a unique set of needed

parameters and status results. The FDC checks to see that the first byte is a valid command and, if valid, proceeds

with the command. If it is invalid, an interrupt is issued. The user sends a Sense Interrupt Status command, which

returns an invalid command error. Refer to Table 17 for explanations of the various symbols used. Table 18 lists the

required parameters and the results associated with each command that the FDC is capable of performing.

Table 17 – Description of Command Symbols

SYMBOL

NAME

DESCRIPTION

Cylinder Address

The currently selected address; 0 to 255.

Data Pattern

The pattern to be written in each sector data field during formatting.

D0, D1

Drive Select 0-1

Designates which drives are perpendicular drives on the

Perpendicular Mode Command. A "1" indicates a perpendicular

drive.

DIR

Direction Control

If this bit is 0, then the head will step out from the spindle during a

relative seek. If set to a 1, the head will step in toward the spindle.

DS0, DS1

Disk Drive Select

DS1

DS0

DRIVE

Drive 0

Drive 1

DTL

Special Sector

Size

By setting N to zero (00), DTL may be used to control the number of

bytes transferred in disk read/write commands. The sector size (N =

0) is set to 128. If the actual sector (on the diskette) is larger than

DTL, the remainder of the actual sector is read but is not passed to

the host during read commands; during write commands, the

remainder of the actual sector is written with all zero bytes. The CRC

check code is calculated with the actual sector. When N is not zero,

DTL has no meaning and should be set to FF HEX.

Enable Count

When this bit is "1" the "DTL" parameter of the Verify command

becomes SC (number of sectors per track).

EFIFO

Enable FIFO

This active low bit when a 0, enables the FIFO. A "1" disables the

FIFO (default).

EIS

Enable Implied

Seek

When set, a seek operation will be performed before executing any

read or write command that requires the C parameter in the

command phase. A "0" disables the implied seek.

EOT

End of Track

The final sector number of the current track.

GAP

Alters Gap 2 length when using Perpendicular Mode.

GPL

Gap Length

The Gap 3 size. (Gap 3 is the space between sectors excluding the

VCO synchronization field).

H/HDS

Head Address

Selected head: 0 or 1 (disk side 0 or 1) as encoded in the sector ID

field.

HLT

Head Load Time

The time interval that FDC waits after loading the head and before

initializing a read or write operation. Refer to the Specify command

for actual delays.

HUT

Head Unload

Time

The time interval from the end of the execution phase (of a read or

write command) until the head is unloaded. Refer to the Specify

command for actual delays.

LOCK

Lock defines whether EFIFO, FIFOTHR, and PRETRK parameters of

the CONFIGURE COMMAND can be reset to their default values by

a "software Reset". (A reset caused by writing to the appropriate bits

of either the DSR or DOR)

MFM

MFM/FM Mode

Selector

A one selects the double density (MFM) mode. A zero selects single

density (FM) mode.

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