PC87332VLJ datasheet(46/98 Pages) NSC

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40 FDC Command Set Description (Continued)

SCAN LOW OR EQUAL

Command Phase

MFM

IPS

DR1

DR0

Track Number

Drive Head Number

Sector Number

Bytes per Sector

End of Track Sector Number

Intersector Gap Length

Sector Step Size

Execution Phase

Data transferred from system to control-

ler is compared to data read from disk

Result Phase

Status Register 0

Status Register 1

Status Register 2

Track Number

Head Number

Sector Number

Bytes per Sector

4116 Seek Command

The Seek command steps the selected drive in or out until

the desired track number is reached During the Execution

Phase of the Seek command the track number to seek to is

compared with the present track number The controller will

determine how many step pulses to issue and the DIR disk

interface output will indicate which direction the RW head

should move The DRx BUSY bit is set in the MSR for the

appropriate drive The controller will wait the Motor On time

before issuing the first step pulse

After the Motor On time the controller will enter the Idle

Phase The execution of the actual step pulses occurs in the

Drive Polling phase of the controller The step pulse rate is

determined by the value programmed in the Specify com-

mand An interrupt will be generated one step pulse period

after the last step pulse is issued A Sense Interrupt com-

mand should be issued to determine the cause of the inter-

rupt There is no Result Phase

While the internal microengine is capable of performing

seek commands on 2 or more drives at the same time soft-

ware should ensure that only one drive is seeking at a time

This is because the drives are actually selected via the

DOR which can only select one drive at a time No other

command except a Sense Interrupt command should be is-

sued while a Seek command is in progress

If the extended track range mode is enabled with the ETR

bit in the Mode command a fourth command byte should be

written in the Command Phase to indicate the four most

significant bits of the desired track number Otherwise only

three command bytes should be written

Command Phase

00001111

XXXXX

DR1

DR0

New Track Number

MSN of Track Number

0000

Note

The last Command Phase byte is required only if ETR is set in Mode

Command

Execution Phase

Disk drive head is stepped in or out to a

programmed track

Result Phase

None

4117 Sense Drive Status Command

The Sense Drive Status command returns the status of the

selected disk drive in ST3 This command does not gener-

ate an interrupt

Command Phase

00000

XXXXXHDDR1

DR0

Execution Phase

Disk drive status information is detected

and reported

Result Phase

Status Register 3

4118 Sense Interrupt Command

The Sense Interrupt command is used to determine the

cause of an interrupt when the interrupt is a result of the

change in status of any disk drive

Command Phase

00001000

Execution Phase

Status of interrupt is reported

Result Phase

Status Register 0

Present Track Number (PTR)

MSN of PTR

0000

Note

The third Result Phase byte can only be read if ETR is set in the Mode

Command

Four possible causes for the interrupt are

1 Entry into the Result Phase of any of the following com-

mands

Read Data

Read Deleted Data

Read a Track

Read ID

Write Data

Write Deleted Data

Format

Scan

Verify

2 Occurrence of a data transfer in the Execution Phase

while in the Non-DMA mode

PC87332VLJ Datasheet(PDF) 46 Page - National Semiconductor (TI)

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