FDC37C78-HT datasheet(29/82 Pages) MICROCHIP

29 / 82 page

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

invalid

command error. Refer to Table 18 or explanations

of the various symbols used. Table 19 lists the

required

parameters and the results associated

with each command that the FDC is capable of

performing.

Table 18 - 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, D2,

Drive Select 0-3

Designates

which

drives

are

perpendicular

drives

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

drive 2

drive 3

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

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