82845PE Datasheet, PDF (82/176 Pages) Intel Corporation – 82845GE Graphics and Memory Controller Hub (GMCH) and 82845PE Memory Controller Hub (MCH)

Register Description
3.5.2.14
IOBASE1—I/O Base Address Register (Device 1)
Address Offset:
Default Value:
Access:
Size:
1Ch
F0h
RO, R/W
8 bits
This register controls the processor to PCI_B/AGP I/O access routing based on the following
formula:
IO_BASE ≤ address ≤ IO_LIMIT
Only the upper 4 bits are programmable. For the purpose of address decode, address bits A[11:0]
are treated as 0. Thus, the bottom of the defined I/O address range will be aligned to a 4-KB
boundary.
3.5.2.15
Bit
Description
7:4
I/O Address Base (IOBASE). Corresponds to A[15:12] of the I/O addresses passed by bridge 1 to
AGP/PCI_B.
3:0 Reserved.
IOLIMIT1—I/O Limit Address Register (Device 1)
Address Offset:
Default Value:
Access:
Size:
1Dh
00h
RO, R/W
8 bits
This register controls the processor to PCI_B/AGP I/O access routing based on the following
formula:
IO_BASE ≤ address ≤ IO_LIMIT
Only the upper 4 bits are programmable. For the purpose of address decode, address bits A[11:0]
are assumed to be FFFh. Thus, the top of the defined I/O address range will be at the top of a 4-KB
aligned address block.
Bit
Description
7:4
I/O Address Limit (IOLIMIT). This field corresponds to A[15:12] of the I/O address limit of Device 1.
Devices between this upper limit and IOBASE1 will be passed to AGP/PCI_B.
3:0 Reserved.
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Intel^® 82845GE/82845PE Datasheet