82845PE Datasheet, PDF (63/176 Pages) Intel Corporation – 82845GE Graphics and Memory Controller Hub (GMCH) and 82845PE Memory Controller Hub (MCH)

Register Description
At the time that a hub interface or AGP accesses to the PAM region may occur, the targeted PAM
segment must be programmed to be both readable and writeable.
As an example, consider BIOS that is implemented on the expansion bus. During the initialization
process, the BIOS can be shadowed in main memory to increase the system performance. When
BIOS is shadowed in main memory, it should be copied to the same address location. To shadow
the BIOS, the attributes for that address range should be set to write only. The BIOS is shadowed
by first doing a read of that address. This read is forwarded to the expansion bus. The host then
does a write of the same address, which is directed to main memory. After the BIOS is shadowed,
the attributes for that memory area are set to read only so that all writes are forwarded to the
expansion bus. Figure 3-4 and Table 3-2 show the PAM registers and the associated attribute bits.
Figure 3-4. PAM Register Attributes
PAM6
PAM5
PAM4
PAM3
PAM2
PAM1
PAM0
Offset
96h
95h
94h
93h
92h
91h
90h
76 5 4
R R WE RE
Reserved
Reserved
Write Enable (R/W)
1=Enable
0=Disable
Read Enable (R/W)
1=Enable
0=Disable
3 21 0
R R WE RE
Read Enable (R/W)
1=Enable
0=Disable
Write Enable (R/W)
1=Enable
0=Disable
Reserved
Reserved
Table 3-2. PAM Register Attributes
PAM Reg
Attribute Bits
PAM0[3:0]
Reserved
PAM0[7:4] R
R
WE
RE
PAM1[3:0] R
R
WE
RE
PAM1[7:4] R
R
WE
RE
PAM2[3:0] R
R
WE
RE
PAM2[7:4] R
R
WE
RE
PAM3[3:0] R
R
WE
RE
PAM3[7:4] R
R
WE
RE
PAM4[3:0] R
R
RE
PAM4[7:4] R
R
WE
RE
PAM5[3:0] R
R
WE
RE
PAM5[7:4] R
R
WE
RE
PAM6[3:0] R
R
WE
RE
PAM6[7:4] R
R
WE
RE
Memory Segment
Comments
0F0000h–0FFFFFh
0C0000h–0C3FFFh
0C4000h–0C7FFFh
0C8000h–0CBFFFh
0CC000h–0CFFFFh
0D0000h–0D3FFFh
0D4000h–0D7FFFh
0D8000h–0DBFFFh
0DC000h–0DFFFFh
0E0000h–0E3FFFh
0E4000h–0E7FFFh
0E8000h–0EBFFFh
0EC000h–0EFFFFh
BIOS Area
ISA Add-on BIOS
ISA Add-on BIOS
ISA Add-on BIOS
ISA Add-on BIOS
ISA Add-on BIOS
ISA Add-on BIOS
ISA Add-on BIOS
ISA Add-on BIOS
BIOS Extension
BIOS Extension
BIOS Extension
BIOS Extension
Offset
90h
90h
91h
91h
92h
92h
93h
93h
94h
94h
95h
95h
96h
96h
Intel^® 82845GE/82845PE Datasheet
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