FDC37N769 datasheet(21/138 Pages) SMSC

21 / 138 page

SMSC DS – FDC37N769

Page 21 of 137

Rev. 12/21/2000

DMAEN, Bit 3

PC/AT and Model 30 Interface Mode

In 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. In PC/AT and Model 30 mode the DMAEN bit is a logic “0” after a reset.

PS/2 Interface Mode

In PS/2 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 the DMAEN bit will be cleared to a logic “0”.

MOTOR ENABLE 0, Bit 4

This bit controls the MTR0 disk interface output. A logic “1” in this bit will cause the output pin to go active.

MOTOR ENABLE 1, Bit 5

This bit controls the MTR1 disk interface output. A logic “1” in this bit will cause the output pin to go active.

MOTOR ENABLE 2, Bit 6

The MOTOR ENABLE 2 bit controls the MTR2 disk interface output. A logic “1” in this bit will cause the output pin to

go active.

MOTOR ENABLE 3, Bit 7

The MOTOR ENABLE 3 bit controls the MTR3 disk interface output. A logic “1” in this bit causes the output to go

active.

Table 10 - Drive Activation Values

DRIVE

DOR VALUE

1CH

2DH

4EH

8FH

Drive Select Encoding

The FDC37N769 can support two types of drive select encoding: Internal 2 Drive decoding (Table 11) and External 2-

to-4 Drive decoding (Table 13). Internal 2 Drive decoding specifies support for a maximum of two floppy drives.

External 2-to-4 Drive decoding expands support for four floppy drives but requires an external 2-to-4 decoder. The

drive select encoding is determined by the EXTx4 bit in CR05.

The FDC37N769 can also internally swap drive 0 and drive 1 using the Swap Drv 0, 1 bit in CR05. Table 12

illustrates Internal 2-Drive decoding with drive 0 and drive 1 swapped. Table 14 illustrates External 2-to-4 Drive

decoding with drive 0 and drive 1 swapped.

Table 11 - Internal 2 Drive Decode: Drives 0 and 1 Not Swapped

DIGITAL OUTPUT REGISTER

DRIVE SELECT OUTPUTS

(ACTIVE LOW)

MOTOR ON OUTPUTS

(ACTIVE LOW)

Bit 7

Bit 6

Bit 5

Bit 4

Bit1

Bit 0

nDS1

nDS0

nMTR1

nMTR0

nBIT 5

nBIT 4

nBIT 5

nBIT 4

nBIT 5

nBIT 4

nBIT 5

nBIT 4

nBIT 5

nBIT 4

FDC37N769 Datasheet(PDF) 21 Page - SMSC Corporation

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