Datasheet

Intel
®
82845G/82845GL/82845GV GMCH Datasheet 65
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.
For details on overall system address mapping scheme, refer to Chapter 5.
Figure 3-4. PAM Register Attributes
Table 3-2. PAM Register Attributes
PAM Reg Attribute Bits Memory Segment Comments Offset
PAM0[3:0] Reserved 90h
PAM0[7:4] R R WE RE 0F0000h–0FFFFFh BIOS Area 90h
PAM1[3:0] R R WE RE 0C0000h–0C3FFFh ISA Add-on BIOS 91h
PAM1[7:4] R R WE RE 0C4000h–0C7FFFh ISA Add-on BIOS 91h
PAM2[3:0] R R WE RE 0C8000h–0CBFFFh ISA Add-on BIOS 92h
PAM2[7:4] R R WE RE 0CC000h–0CFFFFh ISA Add-on BIOS 92h
PAM3[3:0] R R WE RE 0D0000h–0D3FFFh ISA Add-on BIOS 93h
PAM3[7:4] R R WE RE 0D4000h–0D7FFFh ISA Add-on BIOS 93h
PAM4[3:0] R R RE 0D8000h–0DBFFFh ISA Add-on BIOS 94h
PAM4[7:4] R R WE RE 0DC000h–0DFFFFh ISA Add-on BIOS 94h
PAM5[3:0] R R WE RE 0E0000h–0E3FFFh BIOS Extension 95h
PAM5[7:4] R R WE RE 0E4000h–0E7FFFh BIOS Extension 95h
PAM6[3:0] R R WE RE 0E8000h–0EBFFFh BIOS Extension 96h
PAM6[7:4] R R WE RE 0EC000h–0EFFFFh BIOS Extension 96h
REWERE R RWERR
76543210
PAM6
PAM5
PAM4
PAM3
PAM2
PAM1
PAM0
Read Enable (R/W)
1=Enable
0=Disable
Write Enable (R/W)
1=Enable
0=Disable
Reserved
Reserved
Read Enable (R/W)
1=Enable
0=Disable
Write Enable (R/W)
1=Enable
0=Disable
Reserved
Reserved
96h
95h
94h
93h
92h
91h
90h
Offset