FDC37B78X datasheet(21/258 Pages) SMSC

21 / 258 page

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 is 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

BIT 7 MOTOR ENABLE 3

The MTR3 disk interface output is not. (Always

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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