82801DB Datasheet, PDF (316/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

LPC Interface Bridge Registers (D31:F0)
9.2.1
9.2.2
DMABASE_CA—DMA Base and Current Address Registers
I/O Address:
Default Value:
Lockable:
Ch. #0 = 00h; Ch. #1 = 02h
Ch. #2 = 04h; Ch. #3 = 06h
Ch. #5 = C4h Ch. #6 = C8h
Ch. #7 = CCh;
Undef
No
Attribute:
Size:
Power Well:
R/W
16 bit (per channel),
but accessed in two 8-bit
quantities
Core
Bit
Description
Base and Current Address — R/W. This register determines the address for the transfers to be
performed. The address specified points to two separate registers. On writes, the value is stored in
the Base Address register and copied to the Current Address register. On reads, the value is returned
from the Current Address register.
The address increments/decrements in the Current Address register after each transfer, depending
on the mode of the transfer. If the channel is in auto-initialize mode, the Current Address register will
15:0 _{be reloaded from the Base Address register after a terminal count is generated.}
For transfers to/from a 16-bit slave (channel’s 5–7), the address is shifted left one bit location. Bit 15
will be shifted into Bit 16.
The register is accessed in 8-bit quantities. The byte is pointed to by the current byte pointer flip/flop.
Before accessing an address register, the byte pointer flip/flop should be cleared to ensure that the
low byte is accessed first
DMABASE_CC—DMA Base and Current Count Registers
I/O Address:
Default Value:
Lockable:
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:
Power Well:
R/W
16 bit (per channel),
but accessed in two 8-bit
quantities
Core
Bit
Description
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
15:0 ^{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 57), 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.
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Intel^® 82801DB ICH4 Datasheet