PIIX datasheet(64/122 Pages) INTEL

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82371FB (PIIX) AND 82371SB (PIIX3)

2.5.1.6.

DS—DMA Status Register

I/O Address:

Channels 0-3—08h; Channels 4-7—0D0h

Default Value:

00h

Attribute:

Read Only

Each DMA controller has a read-only DMA Status Register that indicates which channels have reached

terminal count and which channels have a pending DMA request.

Bit

Description

7:4

Channel Request Status. When a valid DMA request is pending for a channel (on its DREQ

signal line), the corresponding bit is set to 1. When a DMA request is not pending for a

particular channel, the corresponding bit is set to 0. The source of the DREQ may be hardware

or a software request. Note that channel 4 does not have DREQ or DACK lines, so the

response for a read of DMA2 status for channel 4 is irrelevant.

Bit

Channel

1 (5)

2 (6)

3 (7)

3:0

Channel Terminal Count Status. 1=TC is reached; 0=TC is not reached.

Bit

Channel

1 (5)

2 (6)

3 (7)

2.5.1.7.

DMA Base And Current Address Registers (8237 Compatible Segment)

I/O Address:

DMA Channel 0—000h

DMA Channel 4—0C0h

DMA Channel 1—002h

DMA Channel 5—0C4h

DMA Channel 2—004h

DMA Channel 6—0C8h

DMA Channel 3—006h

DMA Channel 7—0CCh

Default Value:

XXXXh (CPURST or Master Clear)

Attribute:

Read/Write

This Register works in conjunction with the Low Page Register. After an autoinitialization, this register

retains the original programmed value. Autoinitialize takes place after a TC. The address register is

automatically incremented or decremented after each transfer. This register is read/written in

successive 8-bit bytes. The programmer must issue the "Clear Byte Pointer Flip-Flop" command to

reset the internal byte pointer and correctly align the write prior to programming the Current Address

Bit

Description

15:0

Base and Current Address [15:0]. These bits represent address bits [15:0] used when

forming the 24-bit address for DMA transfers.

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