Register Description
R
Intel® 82845 MCH for SDR Datasheet 61
Table 9. 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 BI OS 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
For details on overall system address mapping scheme see Chapter 4.
DOS Application Area (00000h–9FFFh)
The DOS area is 640 KB in size and it is further divided into two parts. The 512 KB area at
0h to 7FFFFh is always mapped to the system memory controlled by the MCH, while the 128 KB
address range from 080000 to 09FFFFh can be mapped to PCI0 or to system memo ry. By default
this range is mapped to system memory and can be declared as a system memory hole (accesses
forwarded to PCI0) via MCH FDHC configura tion register.
Video Buffer Area (A0000h–BFFFFh)
Attribute bits do not control this 128 KB area. The host -initiated cycles in this region are always
forwarded to either PCI0 or AGP unless this range is accessed in SMM mode. Routing of
accesses is controlled by the Legacy VGA control mechanism of the “virtual” PCI-PCI
bridge device embedded within the MCH.
This area can be programmed as SMM area via the SMRAM register. When used as a SMM
space, this range cannot be accessed from the hub interface or AGP.
Expansion Area (C0000h–DFFFFh)
This 128 KB area is divided into eight 16 KB segments, which can be assigned with different
attributes via PAM control register as defined by the table above.