Computer Hardware User Manual

Intel® 460GX Chipset Software Developer’s Manual 11-17
LPC/FWH Interface Configuration
11.2.1.4 WSMB–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].
11.2.1.5 RWAMB–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
7:3 Reserved. Must be 0.
2 Channel 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)
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)