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
0
1
2
3
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
DRIVE SELECT OUTPUTS
(ACTIVE LOW)
MOTOR ON OUTPUTS
(ACTIVE LOW)
DIGITAL OUTPUT REGISTER
Bit 7 Bit 6 Bit 5 Bit 4 Bit1 Bit 0
nDS1
nDS0
nMTR1
nBIT 5
nBIT 5
nBIT 5
nBIT 5
nBIT 5
nMTR0
X
X
X
1
X
X
1
X
1
1
X
X
X
0
0
0
1
1
X
0
1
0
1
X
1
0
1
1
1
0
1
1
1
1
nBIT 4
nBIT 4
nBIT 4
nBIT 4
nBIT 4
X
X
0
X
0
0
Table 12 - Internal 2-Drive Decode: Drive 0 and 1 Swapped
DRIVE SELECT
OUTPUTS (ACTIVE LOW)
MOTOR ON OUTPUTS
(ACTIVE LOW)
DIGITAL OUTPUT REGISTER
Bit 7 Bit 6 Bit 5 Bit 4 Bit1 Bit 0
nDS1
nDS0
nMTR1
nBIT 4
nBIT 4
nBIT 4
nBIT 4
nBIT 4
nMTR0
X
X
X
1
X
X
1
X
1
1
X
X
X
0
0
0
1
1
X
0
1
0
1
X
0
1
1
1
1
1
0
1
1
1
nBIT 5
nBIT 5
nBIT 5
nBIT 5
nBIT 5
X
X
0
X
0
0
Table 13 - External 2-to-4 Drive Decode: Drives 0 and 1 Not Swapped
DRIVE SELECT
OUTPUTS
MOTOR ON
OUTPUTS
DIGITAL OUTPUT REGISTER
(ACTIVE LOW)
(ACTIVE LOW)
Bit 7
Bit 6
Bit 5
Bit 4
Bit1
Bit 0
0
nDS1
nDS0
nMTR1 nMTR0
X
X
X
1
X
X
1
0
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
X
1
X
0
1
1
X
X
1
0
X
X
X
1
1
X
X
X
0
X
X
0
0
0
X
0
X
0
1
0
X
X
1
0
X
X
X
1
1
SMSC DS – FDC37N769
Page 21 of 137
Rev. 02-16-07
DATASHEET
SMSC [ SMSC CORPORATION ]
