PC87317 datasheet(97/272 Pages) NSC

97 / 272 page

The Digital Floppy Disk Controller (FDC) (Logical Device 3)

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Bit 5 - Step

This bit indicates whether or not the head of the Floppy

Disk Drive (FDD) should move during a seek operation.

Its value is the inverse of the STEP disk interface output

signal.

0: STEP is not active, i.e., the head of the FDD

moves. (Default)

1: STEP is active (low), i.e., the head of the FDD does

not move.

Bit 6 - Reserved

Bit 7 - IRQ Pending

This bit signals the completion of the execution phase of

certain FDC commands. Its value reflects the status of

the IRQ signal assigned to the FDC.

0: The IRQ signal assigned to the FDC is not active.

1: The IRQ signal assigned to the FDC is active, i.e.,

the FDD has completed execution of certain FDC

commands.

5.3.2

Status Register B (SRB)

Status Register B (SRB) is a read-only diagnostic register

that is valid only in PS/2 drive mode.

SRB can be read at any time while PS/2 drive mode is ac-

tive. In PC-AT drive mode, all bits are in TRI-STATE during

a microprocessor read.

Bit 0 - Motor 0 Status (MTR0)

This bit indicates the complement of the MTR0 output

pin.

This bit is cleared to 0 by a hardware reset and unaffect-

ed by a software reset.

0: MTR0 not active; motor 0 off

1: MTR0 active; motor 0 on (default)

Bit 1 - Motor 1 Status (MTR1)

This bit indicates the complement of the MTR1 output

pin.

This bit is cleared to 0 by a hardware reset and unaffect-

ed by a software reset.

0: MTR0 not active; motor 1 off

1: MTR0 active.; motor 1 on (default)

Bit 2 - Write Circuitry Status (WGATE)

This bit indicates the complement of the WGATE output

pin.

0: WGATE not active. The write circuitry of the select-

ed FDD is enabled.

1: WGATE active. The write circuitry of the selected

FDD is disabled. (Default))

Bit 3 - Read Data Status (RDATA)

If read data was sent, this bit indicates whether an odd

or even number of bits was sent.

Every inactive edge transition of the RDATA disk inter-

face output signal causes this bit to change state.

0: Either no read data was sent or an even number of

bits of read data was sent. (Default)

1: An odd number of bits of read data was sent.

Bit 4 - Write Data Status (WDATA)

If write data was sent, this bit indicates whether an odd

or even number of bits was sent.

Every inactive edge transition of the WDATA disk inter-

face output signal causes this bit to change state.

0: Either no write data was sent or an even number of

bits of write data was sent. (Default)

1: An odd number of bits of write data was sent.

Bit 5 - Drive Select 0 Status

This bit reflects the status of drive select bit 0 in the Dig-

ital Output Register (DOR). See Section 5.3.3 "Digital

Output Register (DOR)".

It is cleared after a hardware reset and unaffected by a

software reset.

0: Either drive 0 or 2 is selected. (Default)

1: Either drive 1 or 3 is selected.

Bits 7,6 - Reserved

These bits are reserved and are always 1.

5.3.3

Digital Output Register (DOR)

DOR is a read/write register that can be written at any time.

It controls the drive select and motor enable disk interface

output signals, enables the DMA logic and contains a soft-

ware reset bit.

The contents of the DOR is set to 00h after a hardware re-

set, and is unaffected by a software reset.

TABLE 5-2 "Drive and Motor Pin Encoding for Four Drive

Configurations and Drive Exchange Support" shows how

the bits of DOR select a drive and enable a motor when the

FDC is enabled (bit 3 of the Function Enable Register 1

(FER1) at offset 00h of logical device 8 is 1) and bit 7 of the

SuperI/O FDC Configuration register at index F0h is 1. Bit

patterns not shown produce states that should not be de-

coded to enable any drive or motor.

When the FDC is enabled and bit 7 of the of the SuperI/O

FDC Configuration register at index F0h is 1, MTR1 pre-

sents a pulse that is the inverse of WR. This pulse is active

whenever an I/O write to address 02h occurs. This pulse is

delayed for between 25 and 80 nsec after the leading edge

of WR. The leading edge of this pulse can be used to clock

data into an external latch (e.g., 74LS175).

76543210

Reset

Required

SRB Register

Offset 01h

WGATE

WDATA

Drive Select 0 Status

Reserved

MTR0

MTR1

RDATA

PS/2 Drive Mode

PC87317 Datasheet(PDF) 97 Page - National Semiconductor (TI)

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