VT82C686B

Manufacturer Part NumberVT82C686B
ManufacturerETC-unknow
VT82C686B datasheet
 


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Page 54/128:

Floppy Disk Controller Registers

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Super-I/O I/O Ports

Floppy Disk Controller Registers

These registers are located at I/O ports which are offsets from
“FDCBase” (index E3h of the Super-I/O configuration
registers). FDCBase is typically set to allow these ports to be
accessed at the standard floppy disk controller address range
of 3F0-3F7h.
Port FDCBase+2 – FDC Command ................................. RW
7
Motor 3 (unused in VT82C686B: no MTR3# pin)
6
Motor 2 (unused in VT82C686B: no MTR2# pin)
5
Motor 1
0
Motor Off
1
Motor On
4
Motor 0
0
Motor Off
1
Motor On
3
DMA and IRQ Channels
0
Disable
1
Enable
2
FDC Reset
0
Execute FDC Reset
1
FDC Enable
1-0
Drive Select
00 Select Drive 0
01 Select Drive 1
1x -reserved-
Port FDCBase+4 – FDC Main Status ............................... RO
7
Main Request
0
Data register not ready
1
Data register ready
6
Data Input / Output
0
CPU => FDC
1
FDC => CPU
5
Non-DMA Mode
0
FDC in DMA mode
1
FDC not in DMA mode
4
FDC Busy
0
FDC inactive
1
FDC active
3-2
Reserved
........................................ always reads 0
1
Drive 1 Active
0
Drive inactive
1
Drive performing a positioning change
0
Drive 0 Active
0
Drive inactive
1
Drive performing a positioning change
Revision 1.71 June 9, 2000
Port FDCBase+4 – FDC Data Rate Select ...................... WO
7
Software Reset
0
Normal operation................................... default
1
Execute FDC reset (this bit is self clearing)
6
Power Down
0
Normal operation................................... default
1
Power down FDC logic
........................................always reads 0
5
Reserved
4-2
Precompensation Select
Selects the amount of write precompensation to be
used on the WDATA output:
000 Default ................................................... default
001 41.7 ns
010 93.3 ns
011 125.0 ns
100 166.7 ns
101 208.3 ns
110 250.0 ns
111 0.0 ns (disable)
1-0
Data Rate
MFM FM
00
500K 250K bps 1.2MB 5” or 1.44 MB 3”
01
300K 150K bps 360KB 5”
10
250K 125K bps 720KB 3” ................ default
11
1M illegal bps
Note: these bits are not changed by software reset
Port FDCBase+5 – FDC Data .......................................... RW
Port FDCBase+7 – FDC Disk Change Status ................. RW
7
Disk Change ......................................................... RO
0
Floppy not changed................................ default
1
Floppy changed since last instruction
6-2
Undefined
..................................... always reads 1’s
1-0
Data Rate
........................................................ WO
00 500 Kbit/sec (1.2MB 5” or 1.44 MB 3” drive)
01 300 Kbit/sec (360KB 5” drive)
10 250 Kbit/sec (720KB 3” drive)
11 1 Mbit/sec
-48-
Register Descriptions - Super-I/O I/O Ports
VT82C686B
Drive Type