E
4.2.1.9.
82371AB (PIIX4)
73
4/9/97 2:23 PM PIIX4aDS
INTEL CONFIDENTIAL
(until publication date)
PRELIMINARY
DLPAGE—DMA Low Page Registers (IO)
I/O Address:
DMA Channel 0—087h
DMA Channel 1—083h
DMA Channel 2—081h
DMA Channel 3—082h
Undefined (CPURST or Master Clear)
Read/Write
DMA Channel 5—08Bh
DMA Channel 6—089h
DMA Channel 7—08Ah
Default Value:
Attribute:
This register works in conjunction with the Current Address Register. After an autoinitialization, this register
retains the original programmed value. Autoinitialize takes place after a TC.
Bit
Description
7:0
DMA Low Page [23:16].
These bits represent address bits [23:16] of the 24-bit DMA address.
4.2.1.10.
DCBP—DMA Clear Byte Pointer Register (IO)
I/O Address:
Default Value:
Attribute:
Channels 0–3—00Ch; Channels 4–7—0D8h
All bits undefined
Write Only
Writing to this register executes the Clear Byte Pointer Command. This command is executed prior to
reading/writing a new address or word count to the DMA. The command initializes the byte pointer flip-flop to a
known state so that subsequent accesses to register contents address upper and lower bytes in the correct
sequence. The Clear Byte Pointer Command (or CPURST or the Master Clear Command) clears the internal
latch used to address the upper or lower byte of the 16-bit Address and Word Count Registers.
Bit
Description
7:0
Clear Byte Pointer.
No specific pattern. Command enabled with a write to the I/O port address.
4.2.1.11.
DMC—DMA Master Clear Register (IO)
I/O Address:
Default Value:
Attribute:
Channel 0–3—00Dh; Channel 4–7—0DAh
All bits undefined
Write Only
This software instruction has the same effect as the hardware Reset.
Bit
Description
7:0
Master Clear.
No specific pattern. Command enabled with a write to the I/O port address.