PC87306 datasheet(46/110 Pages) NSC

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40 FDC Command Set Description (Continued)

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

3 The Ready Signal changed state during the polling mode

for an internally selected drive (Occurs only after a hard-

ware or software reset)

4 A Seek Relative Seek or Recalibrate command termi-

nates

An interrupt due to reasons 1 or 2 does not require the

Sense Interrupt command and is cleared automatically This

type of interrupt occurs during normal command operations

and is easily discernible by the mP via the MSR It is cleared

when reading or writing information from or to the Data Reg-

ister (FIFO)

An interrupt caused by reasons 3 or 4 is identified with the

aid of the Sense Interrupt command This type of interrupt is

cleared after the first result byte has been read Use bits 5

6 and 7 of ST0 to identify the cause of the interrupt as

shown in Table 4-14

Issuing a Sense Interrupt command without an interrupt

pending is treated as an Invalid command If the extended

track range mode is enabled a third byte should be read in

the Result Phase which will indicate the four most signifi-

cant bits of the present track number Otherwise only two

result bytes should be read

TABLE 4-14 Status Register 0 Termination Codes

Status Register 0

Cause

Interrupt

Seek

Code

End

Internal Ready Went True

Normal Seek Termination

Abnormal Seek Termination

4119 Set Track Command

This command is used to inspect or change the value of the

internal Present Track Register This can be useful for re-

covery from disk mistracking errors where the real current

track can be read through the Read ID command and then

the Set Track command can be used to set the internal

Present Track Register to the correct value

If the WNR bit is a 0 a track register is to be read In this

case the Result Phase byte contains the value in the inter-

nal register specified and the third byte in the Command

Phase is a dummy byte

If the WNR bit is a 1 data is written to a track register In this

case the third byte of the Command Phase is written to the

specified internal track register and the Result Phase byte

contains this new value

The DS1 and DS0 bits select the Present Track Register for

the particular drive The internal register address depends

on MSB DS1 and DS0 as shown in Table 4-15 This com-

mand does not generate an interrupt

PC87306 Datasheet(PDF) 46 Page - National Semiconductor (TI)

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