FDC37C93 datasheet(21/280 Pages) SMSC

21 / 280 page

DIGITAL OUTPUT REGISTER (DOR)

Address 3F2 READ/WRITE

The DOR controls the drive select and motor

enables

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 four drive

selects DS0 -DS3, 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. When this bit is a a

logic "0" it disables the nDACK and TC inputs and

holds 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

This bit controls the MTR2 disk interface output. A

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

active.

BIT 7 MOTOR ENABLE 3

This bit controls the MTR3 disk interface output. A

logic "1" in this bit causes the output to go active.

Table 3 - Drive Activation Values

MOT

EN3

MOT

EN2

MOT

EN1

MOT

EN0

DMAEN nRESE

DRIVE

SEL1

DRIVE

SEL0

RESET

COND.

DRIVE

DOR VALUE

1CH

2DH

4EH

8FH

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