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FDC37C78

Floppy Disk Controller

SMSC -> Microchip 

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

contains a software reset bit. The contents of the

DOR are unaffected by a software reset. The

DOR can be written to at any time.

RESET

COND.

7

MOT

EN3

0

6

MOT

EN2

0

5

MOT

EN1

0

4

MOT

EN0

0

3

DMAEN

0

2

1

nRESET DRIVE

SEL1

0

0

0

DRIVE

SEL0

0

BIT 0 and 1 DRIVE SELECT

These two bit a 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

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

nDACK, TC and IRQ outputs. This bit being a

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

and hold the DRQ and IRQ outputs in a high

impedance state. This bit is a logic "0" after a

reset and in these modes.

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

DRIVE

DOR VALUE

0

1CH

1

2DH

2

4EH

3

8FH

12

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