PC87303 datasheet(35/114 Pages) NSC

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40 FDC Command Set Description (Continued)

Command Phase

0011

0000

EIS

FIFO

POLL

THRESH

PRETRK

Execution Phase

Internal registers written

Result Phase

None

EIS

Enable Implied Seeks Default after a software reset

0 e Implied seeks disabled through Configure com-

mand Implied seeks can still be enabled through

the Mode command when EIS e 0

1 e

Implied seeks enabled for a read write scan or

verify operation A seek and sense interrupt oper-

ation is performed prior to the execution of the

read write scan or verify operation The IPS bit

does not need to be set

FIFO

Enable FIFO for Execution Phase data transfers De-

fault after a software reset if the LOCK bit is 0 If the

LOCK bit is 1 then the FIFO bit retains its previous

value after a software reset

0 e

FIFO enabled for both reads and writes

1 e FIFO disabled

POLL

Disable for Drive Polling Mode Default after a soft-

ware reset

0 e Enable drive polling mode An interrupt is gener-

ated after a reset

1 e

Disable drive polling mode If the Configure

command is issued within 500 ms of a hardware

or software reset then an interrupt is not gener-

ated In addition the use of the four Sense In-

terrupt commands to clear the ‘‘Ready Changed

State’’ of the four logical drives is not required

THRESH

The FIFO threshold in the Execution Phase of

read and write data transfers

Programmable

from 00h to 0Fh Defaults to 00h after a software

reset if the LOCK bit is 0 If the LOCK bit is 1

THRESH retains its value

A high value of

THRESH is suited for slow response systems

and a low value of THRESH is better for fast re-

sponse systems

PRETRK

Starting track number for write precompensation

Programmable from track 0 (‘‘00’’) to track 255

(‘‘FF’’) Defaults to track 0 (‘‘00’’) after a software

reset if the LOCK bit is 0 If the LOCK bit is 1

then PRETRK retains its value

412 Dumpreg Command

The Dumpreg command is designed to support system run-

time diagnostics application software development and de-

bug This command has a one-byte command phase and a

10-byte result phase The Result Phase returns the values

of parameters set in other commands That is the PTR

(Present Track Register) contains the least significant byte

of the track the microcode has stored for each drive The

Step Rate Time Motor Off and Motor On Times and the

DMA bit are all set in the Specify command

The sixth byte of the result phase varies depending on what

commands have been previously executed If a format com-

mand has previously been issued and no reads or writes

have been issued since then this byte contains the Sectors

per track value If a read or a write command has been

executed more recently than a format command this byte

contains the End of Track value The LOCK bit is set in the

Lock command The eighth result byte also contains the bits

programmed in the Perpendicular Mode command The last

two bytes of the Dumpreg Result Phase are set in the Con-

figure command After a hardware or software reset the

parameters in the result bytes are set to their appropriate

default values

Note

Some of these parameters are unaffected by a software reset de-

pending on the state of the LOCK bit See the Lock Command for

further information

Command Phase

00001110

Execution Phase

Internal registers read

Result Phase

PTR Drive 0

PTR Drive 1

PTR Drive 2

PTR Drive 3

Step Rate Time

Motor Off Time

Motor On Time

DMA

Sector per TrackEnd of Track (Note)

LOCK

DC3

DC2

DC1

DC0

GAP

EIS

FIFO

POLL

THRESH

PRETRK

Note

Sectors per Track parameter returned if last command issued was

Format End of Track parameter returned if last command issued was

Read or Write

413 Format Track Command

This command formats one track on the disk in IBM ISO or

Perpendicular format After the index hole is detected data

patterns are written on the disk including all gaps Address

Marks Address Fields and Data Fields The exact format is

determined by the following parameters

1 The MFM bit in the Opcode (first command) byte which

determines the format of the Address Marks and the en-

coding scheme

2 The IAF bit in the Mode command which selects be-

tween IBM and ISO format

3 The WGATE and GAP bits in the Perpendicular Mode

command which select between the conventional and

Toshiba Perpendicular format

4 The Bytes per Sector code which determines the sector

size

5 The Sector per Track parameter which determines how

many sectors are formatted on the track

6 The Data Pattern byte which is used as the filler byte in

the Data Field of each sector

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