
44
PRELIMINARY
82454KX/GX (PB)
A
2.4.22 PAM[0:6]—PROGRAMMABLE ATTRIBUTE MAP REGISTER
Address Offset:
PAM0 (59h)—PAM6 (5Fh)
Default:
PAM0—30h; PAM[1:6]—33h (82454KX)
Read/Write
These seven registers select read only (RE=1, WE=0), write only (RE=0, WE=1), or read/write (RE=1, WE=1)
access attributes for 14 memory regions between the 512 Kbyte and 1 Mbyte address range. The individual
memory regions can also be disabled (RE=0, WE=0). Each register controls two regions; bits [7:4] control one
region and bits [3:0] control the other region. Note that the default for the system BIOS region is read/write
enabled. The default for all other regions is read/write disabled.
When a region is enabled, the corresponding host bus access is forwarded to PCI; the corresponding PCI
access is ignored (not forwarded to the host bus). When a region is disabled, the corresponding host bus
access is ignored (not forwarded to the PCI bus); the corresponding PCI access is forwarded to the host bus.
Note that the MC has corresponding PAM registers. Only one device (MC/PB) should have the same space
enabled at one time to avoid access conflicts.
PAM
Attribute Bits
Memory Segment
Comments
Offset
Register
7,3
6,2
5,1
4,0
PAM0[7:4]
Reserved
WE
RE
0F0000–0FFFFFh
BIOS
59h
PAM0[3:0]
Reserved
WE
RE
080000–09FFFFh
512–640 KB
59h
PAM1[7:4]
Reserved
WE
RE
0C4000–0C7FFFh
ISA Expansion
5Ah
PAM1[3:0]
Reserved
WE
RE
0C0000–0C3FFFh
ISA Expansion
5Ah
PAM2[7:4]
Reserved
WE
RE
0CC000–0CFFFFh
ISA Expansion
5Bh
PAM2[3:0]
Reserved
WE
RE
0C8000–0CBFFFh
ISA Expansion
5Bh
PAM3[7:4]
Reserved
WE
RE
0D4000–0D7FFFh
ISA Expansion
5Ch
PAM3[3:0]
Reserved
WE
RE
0D0000–0D3FFFh
ISA Expansion
5Ch
PAM4[7:4]
Reserved
WE
RE
0DC000–0DFFFFh
ISA Expansion
5Dh
PAM4[3:0]
Reserved
WE
RE
0D8000–0DBFFFh
ISA Expansion
5Dh
PAM5[7:4]
Reserved
WE
RE
0E4000–0E7FFFh
BIOS Extension
5Eh
PAM5[3:0]
Reserved
WE
RE
0E0000–0E3FFFh
BIOS Extension
5Eh
PAM6[7:4]
Reserved
WE
RE
0EC000–EFFFFh
BIOS Extension
5Fh
PAM6[3:0]
Reserved
WE
RE
0E8000–0EBFFFH
BIOS Extension
5Fh
PAM0—30h (Compatibility PB), 00h (Auxiliary PB)
PAM[1:6]—33h (Compatibility PB), 00h (Auxiliary PB)
For the 450GX, the default for the system BIOS region in the Compatibility PB is read/write enabled. The
default for the auxiliary PB is read/write disabled.