82443GX Datasheet, PDF (45/128 Pages) Intel Corporation – Intel 440GX AGPset: 82443GX Host Bridge/Controller

Register Description
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. Table 3-3 shows the PAM registers and the associated attribute bits:
Table 3-3. PAM Registers and Associated Memory Segments
PAM Reg
PAM0[3:0]
PAM0[7:4]
PAM1[3:0]
PAM1[7:4]
PAM2[3:0]
PAM2[7:4]
PAM3[3:0]
PAM3[7:4]
PAM4[3:0]
PAM4[7:4]
PAM5[3:0]
PAM5[7:4]
PAM6[3:0]
PAM6[7:4]
Attribute Bits
Reserved
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
R R WE RE
Memory Segment
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
Comments
BIOS Area
ISA Add-on BIOS¹
ISA Add-on BIOS¹
ISA Add-on BIOS¹
ISA Add-on BIOS¹
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
59h
59h
5Ah
5Ah
5Bh
5Bh
5Ch
5Ch
5Dh
5Dh
5Eh
5Eh
5Fh
5Fh
NOTE:
1. The C0000h to CFFFFh segment can be used for SMM space if enabled by the SMRAM register
DOS Application Area (00000h–9FFFh)
The DOS area is 640 KB and it is further divided into two parts. The 512 KB area at 0 to 7FFFFh is
always mapped to the main memory controlled by the 82443GX, while the 128 KB address range
from 080000 to 09FFFFh can be mapped to PCI or to main DRAM. By default this range is
mapped to main memory and can be declared as a main memory hole (accesses forwarded to PCI)
via 82443GX’s FDHC configuration register.
Video Buffer Area (A0000h–BFFFFh)
This 128 KB area is not controlled by attribute bits. The host-initiated cycles in this region are
always forwarded to either PCI 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-to-PCI bridge
device embedded within the 82443GX.
This area can be programmed as SMM area via the SMRAM register. When used as a SMM space
this range can not be accessed from PCI 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 Table 3-3.
Extended System BIOS Area (E0000h–EFFFFh)
This 64 KB area is divided into four 16 KB segments which can be assigned with different
attributes via PAM control register as defined by the Table 3-3.
System BIOS Area (F0000h–FFFFFh)
This area is a single 64 KB segment which can be assigned with different attributes via PAM
control register as defined by the Table 3-3.
82443GX Host Bridge Datasheet
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