Intel
82801BA ICH2 Datasheet
9-25
LPC Interface Bridge Registers (D31:F0)
9.2.2
DMABASE_CC—DMA Base and Current Count Registers
I/O Address:
Ch. #0 = 01h; Ch. #1 = 03h
Ch. #2 = 05h; Ch. #3 = 07h
Ch. #5 = C6h; Ch. #6 = CAh
Ch. #7 = CEh;
Undefined
No
Attribute:
Size:
R/W
16-bit (per channel),
but accessed in two 8-bit
quantities
Default Value:
Lockable:
Power Well:
Core
9.2.3
DMAMEM_LP—DMA Memory Low Page Registers
I/O Address:
Ch. #0 = 87h; Ch. #1 = 83h
Ch. #2 = 81h; Ch. #3 = 82h
Ch. #5 = 8Bh; Ch. #6 = 89h
Ch. #7 = 8Ah;
Undefined
No
Attribute:
Size:
Power Well:
R/W
8-bit
Core
Default Value:
Lockable:
Bit
Description
15:0
Base and Current Count
—R/W.
This register determines the number of transfers to be performed.
The address specified points to two separate registers. On writes the value is stored in the
Base
Count
register and copied to the
Current Count
register. On reads the value is returned from the
Current Count
register.
The actual number of transfers is one more than the number programmed in the Base Count Register
(i.e., programming a count of 4h results in 5 transfers). The count is decrements in the Current Count
register after each transfer. When the value in the register rolls from zero to FFFFh, a terminal count
is generated. If the channel is in auto-initialize mode, the Current Count register will be reloaded from
the Base Count register after a terminal count is generated.
For transfers to/from an 8-bit slave (channels 0–3), the count register indicates the number of bytes to
be transferred. For transfers to/from a 16-bit slave (channels 5–7), the count register indicates the
number of words to be transferred.
The register is accessed in 8 bit quantities. The byte is pointed to by the current byte pointer flip/flop.
Before accessing a count register, the byte pointer flip/flop should be cleared to ensure that the low
byte is accessed first.
Bit
Description
7:0
DMA Low Page (ISA Address bits [23:16])
—R/W. This register works in conjunction with the DMA
controller's Current Address Register to define the complete 24-bit address for the DMA channel.
This register remains static throughout the DMA transfer.
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