Intel 460GX manual Dcm-Dma Channel Mode Register I/O, Dr-Dma Request Register I/O

LPC/FWH Interface Configuration

11.2.1.2Dcm–Dma Channel Mode Register (I/O)

I/O Address:	Channels 0-3=0Bh; Channels 4-7=0D6h
Default Value:	Bits[7:2]=0; Bits[1:0]=undefined (CPURST or Master Clear)
Attribute:	Write Only

Each channel has a 6-bit DMA Channel Mode Register. The Channel Mode Registers provide control over DMA transfer type, transfer mode, address increment/decrement, and auto- initialization.

Bit		Description
7:6	DMA Transfer Mode. Each DMA channel can be programmed in one of four different modes:
	Bits[7:6] Transfer Mode
	00 Demand Mode
	01	Single Mode
	10 Block Mode
	11 I Cascade Mode
5	Address Increment/Decrement Select. 0=Increment; 1=Decrement.
4	Auto-initialize Enable. 1=Enable; 0=Disable.
3:2	DMA Transfer Type. When Bits [7:6]=11, the transfer type bits are irrelevant.
	Bits[3:2] Transfer Type
	00	Verify transfer
	01	Write transfer
	10	Read transfer
	11 I Illegal
1:0	DMA Channel Select. Bits [1:0] select the DMA Channel Mode Register written to by bits [7:2].
	Bits[1:0] Channel
	00	Channel 0 (4)
	01	Channel 1 (5)
	10	Channel 2 (6)
	11 Channel 3 (7)

11.2.1.3Dr–Dma Request Register (I/O)

I/O Address:	Channels 0-3–09h; Channels 4-7–0D2h
Default Value:	Bits[1:0]=undefined; Bits[7:2]=0 (CPURST or Master Clear)
Attribute:	Write Only

The Request Register is used by software to initiate a DMA request. The DMA responds to the software request as though DREQx is asserted. These requests are non-maskable and subject to prioritization by the priority encoder network. For a software request, the channel must be in Block Mode. The Request Register status for DMA1 and DMA2 is output on bits [7:4] of a Status Register read.

Bit		Description
7:3	Reserved. Must be 0
2	DMA Channel Service Request. 0=Resets the individual software DMA channel request bit.
	1=Sets the request bit. Generation of a TC also sets this bit to 0.
1:0	DMA Channel Select. Bits [1:0] select the DMA channel mode register to program with bit 2.
	Bits[1:0] Channel
	00	Channel 0
	01	Channel 1 (5)
	10	Channel 2 (6)
	11	Channel 3 (7)

11-16 Intel® 460GX Chipset Software Developer’s Manual