Intel 460GX manual WSMB-Write Single Mask Bit I/O, RWAMB-Read / Write All Mask Bits I/O

LPC/FWH Interface Configuration

11.2.1.4WSMB–Write Single Mask Bit (I/O)

I/O Address:	Channels 0-3–0Ah; Channels 4-7–0D4h
Default Value:	Bits[1:0]=undefined; Bit 2=1; Bits[7:3]=0 (CPURST or a Master Clear)
Attribute:	Write Only

A channel's mask bit is automatically set when the Current Byte/Word Count Register reaches terminal count (unless the channel is programmed for auto-initialization). Setting the entire register disables all DMA requests until a clear mask register instruction allows them to occur. This instruction format is similar to the format used with the DMA Request Register. Masking DMA channel 4 (DMA controller 2, channel 0) also masks DMA channels [3:0].

Bit	Description
7:3	Reserved. Must be 0.

2Channel Mask Select. 1=Disable DREQ for the selected channel. 0=Enable DREQ for the selected channel.

1:0	DMA Channel Select. Bits [1:0] select the DMA Channel Mode Register for bit 2.
	Bits[1:0] Channel
	00 Channel 0 (4)
	01 Channel 1 (5)
	10 Channel 2 (6)
	11 Channel 3 (7)

11.2.1.5RWAMB–Read / Write All Mask Bits (I/O)

I/O Address:	Channels 0-3–0Fh; Channels 4-7–0DEh
Default Value:	Bit[3:0]=1111; Bit[7:4]=0000 (CPURST or Master Clear)
Attribute:	Read/Write

A channel's mask bit is automatically set to 1 when the Current Byte/Word Count Register reaches terminal count (unless the channel is programmed for auto-initialization). Setting bits [3:0] to 1 disables all DMA requests until a clear mask register instruction enables the requests. Note that, masking DMA channel 4 (DMA controller 2, channel 0), masks DMA channels [3:0]. Also note that, Masking DMA controller 2 with a write to port 0DEh also masks DREQ assertions from DMA controller 1.

Bit	Description
7:4	Reserved. Must be 0.
3:0	Channel Mask Bits. 1=Disable the corresponding DREQ(s); 0=Enable the corresponding
	DREQ(s).
	Bit Channel
	0 0 (4)
	1 1 (5)
	2 2 (6)
	3 3 (7)

Intel® 460GX Chipset Software Developer’s Manual 11-17