3 BIOS Overview
BIOS Addresses
38
DMA Channel Controllers
Only “I/O-to-memory” and “memory-to-I/O” transfers are allowed.
“I/O-to-I/O” and “memory-to-memory” transfers are disallowed by the
hardware configuration.
The system controller supports seven DMA channels, each with a page
register used to extend the addressing range of the channel to 16 MB.
The following table summarizes how the DMA channels are allocated.
03B0 - 03DF VGA
03E8 - 03EF COM3
03F0h- 03F5 Floppy disk drive controller
03F6 IDE primary channel
03F7 Floppy disk drive controller
03F8 - 03FF COM1
04D0 - 04D1 Interrupt edge/level control
0678 - 067B LPT2 ECP
0778 - 077B LPT1 ECP
0CF8 - 0CFF PCI configuration space
I/O Address Ports Function
DMA controller
Channel Function
0Free
1 Free if not used for parallel port or audio in Setup
1
2 Floppy disk controller
3 Free if not used for parallel port or audio in
Setup
2
4 Used to cascade DMA channels 0-3
5Free
6Free
7Free
1. DMA 1 is used for the parallel port by default
2. DMA 3 is used by audio by default
Applies only if a
supplementary ISA
card is installed
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