82374EB datasheet(59/208 Pages) INTEL

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82374EB82374SB

Bit

Description

Reserved

Must be 0

DMA Channel Mask SetClear

Writinga1tobit2 sets the mask bit and disables the incoming DREQ

for the selected channel Writinga0tobit2 clears the mask bit and enables the incoming DREQ for

the elected channel

DMA Channel Select

Bits 10 select the DMA Channel Mode Register to program with bit 2

Bits 10

Channel

Channel 0 (4)

Channel 1 (5)

Channel 2 (6)

Channel 3 (7)

326 WAMBWRITE ALL MASK BITS REGISTER

0FhChannels 0-3

0DEhChannels 4-7

Default Value

0Fh

Attribute

ReadWrite

Size

8 Bits

This command allows enabling and disabling of incoming DREQ assertions by writing the mask bits for each

controller DMA1 or DMA2 simultaneously rather than by individual channel as is done with the ‘‘Write Single

Mask Bit’’ command Two registers store the current mask status for DMA1 and DMA2 Setting the mask bit

disables the incoming DREQ x for that channel Clearing the mask bit enables the incoming DREQ x Unlike

the ‘‘Write Single Mask Bit’’ command this command includes a status read to check the current mask status

of the selected DMA channel group When read the mask register current status appears on bits 30

channel’s mask bit is automatically set when the Current Word Count register reaches terminal count (unless

the channel is programmed for autoinitialization) The entire register is also set by a reset or a Master Clear

Setting the entire register disables all DMA requests until a clear Mask register instruction allows them to

occur

Two important points should be taken into consideration when programming the mask registers First individu-

ally masking DMA Channel 4 (DMA controller 2 Channel 0) will automatically mask DMA Channels 30

this channel group is logically cascaded onto Channel 4 Second masking off DMA controller 2 with a write to

port 0DEh will also mask off DREQ assertions from DMA controller 1 for the same reason when DMA Channel

4 is masked so are DMA Channels 0-3

82374EB датащи(PDF) 59 Page - Intel Corporation