FDC37B78X datasheet(21/249 Pages) SMSC

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DIGITAL OUTPUT REGISTER (DOR)

Address 3F2 READ/WRITE

The DOR controls the drive select and motor enables of the disk interface outputs. It also contains the

enable for the DMA logic and a software reset bit. The contents of the DOR are unaffected by a software

reset. The DOR can be written to at any time.

BIT 0 and 1 DRIVE SELECT

These two bits are binary encoded for the drive

selects, thereby allowing only one drive to be

selected at one time.

BIT 2 nRESET

A logic "0" written to this bit resets the Floppy disk

controller. This reset will remain active until a logic

"1" is written to this bit. This software reset does

not affect the DSR and CCR registers, nor does it

affect the other bits of the DOR register.

The

minimum

reset

duration

required

100ns,

therefore toggling this bit by consecutive writes to

this register is a valid method of issuing a software

reset.

BIT 3 DMAEN

PC/AT and Model 30 Mode:

Writing this bit to logic "1" will enable the DRQ,

nDACK, TC and FINTR outputs. This bit being a

logic "0" will disable the nDACK and TC inputs,

and hold the DRQ and FINTR outputs in a high

impedance state.

This bit is a logic "0" after a

reset and in these modes.

PS/2 Mode: In this mode the DRQ, nDACK, TC

and FINTR pins are always enabled.

During a

reset, the DRQ, nDACK, TC, and FINTR pins will

remain enabled, but this bit will be cleared to a

logic "0".

BIT 4 MOTOR ENABLE 0

This bit controls the MTR0 disk interface output. A

logic "1" in this bit will cause the output pin to go

active.

BIT 5 MOTOR ENABLE 1

This bit controls the MTR1 disk interface output. A

logic "1" in this bit will cause the output pin to go

active.

BIT 6 MOTOR ENABLE 2

The MTR2 disk interface output is not. (Always 0)

BIT 7 MOTOR ENABLE 3

The MTR3 disk interface output is not. (Always 0)

Table 6 - Drive Activation Values

DRIVE

DOR VALUE

1CH

2DH

MOT

EN3

MOT

EN2

MOT

EN1

MOT

EN0

DMAEN

nRESE

DRIVE

SEL1

DRIVE

SEL0

RESET

COND.

FDC37B78X Datasheet(PDF) 21 Page - SMSC Corporation

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