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2 Summary of the HP/Phoenix BIOS
Overview of Address Space
Addressing System Board Components
This section provides more details of how the BIOS uses the system board
components mentioned in the I/O port list.
DMA Channel Controllers
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
only types of DMA transfer allowed are:
“I/O-to-memory” and “memory-to-I/O”
“I/O-to-I/O” and “memory-to-memory” transfers are disallowed by the
hardware configuration. The following table summarizes how the DMA
channels are allocated.
First DMA controller (used for 8-bit transfers)
Channel
Function
0
Free
1
Free if not used for parallel port or sound board
2
Flexible disk drive controller
3
Free if not used for parallel port or sound board
Second DMA controller (used for 16-bit transfers)
Channel
Function
4
Used to cascade DMA channels 0-3
5
Free if not used for sound board
6
Free
7
Free if not used for sound board
