PC87309VLJ datasheet(72/192 Pages) NSC

72 / 192 page

The Floppy Disk Controller (FDC) (Logical Device 0)

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When SENSE INTERRUPT is not Necessary

Interrupts that occur during most command operations do

not need to be identified by the SENSE INTERRUPT. The

microprocessor can identify them by checking the Request

for Master (RQM) bit (bit 7) of the Main Status Register

(MSR). See “Bit 7 - Request for Master (RQM)” on page 42.

It is not necessary to issue a SENSE INTERRUPT com-

mand to detect the following causes of Interrupts:

The result phase of any of the following commands

started:

— READ DATA, READ DELETED DATA, READ A

TRACK, READ ID

— WRITE DATA, WRITE DELETED

— FORMAT TRACK

— SCAN EQUAL, SCAN EQUAL OR LOW, SCAN

EQUAL OR HIGH

— VERIFY

Data is being transferred in non-DMA mode, during the

execution phase of some command.

Interrupts caused by these conditions are cleared automat-

ically, or by reading or writing information from or to the

Data Register (FIFO).

Command Phase

Execution Phase

Status of interrupt is reported.

Result Phase.

When bit 2 of the second command phase byte (ETR) in the

MODE command is set to 1, the track number is stored as

a 12-bit value. See “Bit 0 - Extended Track Range (ETR)”

on page 60.

In this case, a third result byte should be read to hold the

Most Significant Nibble (MSN), i.e., the four most significant

bits, of the number of the current track.

Otherwise (ETR bit in MODE is 0), this command phase

byte is not required. and, only two result phase bytes should

be read First Command Phase Byte, Result Phase

Status Register 0

See Section 3.5.1 on page 48.

Second Command Phase Byte,

Present Track Number (PTR)

The value in this byte is the number of the current track.

Fourth Command Phase Byte,

Bits 7-4 - MSN of Track Number

If the track number is stored as a 12-bit value, these bits

contain the Most Significant Nibble (MSN), i.e., the four

most significant bits, of the number of the track to seek.

Otherwise (the ETR bit in the MODE command is 0), this

result phase byte is not required.

3.7.20

The SET TRACK Command

This command is used to verify (read) or change (write) the

number of the present track.

This command could be useful for recovery from disk track-

ing errors, where the true track number could be read from

the disk using the READ ID command, and used as input to

the SET TRACK command to correct the Present Track

number (PTR) stored internally.

Terminating this command does not generate an interrupt

Command Phase

When bit 2 of the second command phase byte (ETR) in the

MODE command is set to 1, the track number is stored as

a 12-bit value. See “Bit 0 - Extended Track Range (ETR)”

on page 60.

In this case, issue SET TRACK twice - once for the Most

Significant Byte (MSB) of the number of the current track

and once for the Least Significant Byte (LSB).

Otherwise (ETR bit in MODE is 0), issue SET TRACK only

once, with bit 2 (MSB) of the second command phase byte

set to 0.

TABLE 3-21. Interrupt Causes Reported by SENSE

INTERRUPT

Bits of

ST0

Interrupt Cause

0 FDC became ready during drive polling mode.

SEEK, RELATIVE SEEK or RECALIBRATE

not completed.

1 SEEK, RELATIVE SEEK or RECALIBRATE

terminated normally.

1 SEEK, RELATIVE SEEK or RELCALIBRATE

terminated abnormally.

76543210

00001000

76543210

Result Phase Status Register 0 (ST0)

Byte of Present Track Number (PTR)

MSN of PTR

76543210

WNR

100001

00110

MSB

DS1

DS0

Byte of Present Track Number (PTR)

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