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System Address Map
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100 Intel
®
82845 MCH for SDR Datasheet
4.1.2 PAM Memory Spaces
The address ranges in this memory space are:
• PAMC0 0_000C_0000 to 0_000C_3FFF
• PAMC4 0_000C_4000 to 0_000C_7FFF
• PAMC8 0_000C_8000 to _000C_BFFF
• PAMCC 0_000C_C000 to 0_000C_FFFF
• PAMD0 0_000D_0000 to 0_000D_3FFF
• PAMD4 0_000D_4000 to 0_000D_7FFF
• PAMD8 0_000D_8000 to 0_000D_BFFF
• PAMDC 0_000D_C000 to 0_000D_FFFF
• PAME0 0_000E_0000 to 0_000E_3FFF
• PAME4 0_000E_4000 to 0_000E_7FFF
• PAME8 0_000E_8000 to 0_000E_BFFF
• PAMEC 0_000E_C000 to 0_000E_FFFF
• PAMF0 0_000F_0000 to 0_000F_FFFF
The 256 KB PAM region is divided into three parts:
• ISA expansion region; 128 KB area between 0_000C_0000h–0_000D_FFFFh
• Extended BIOS region; 64 KB area between 0_000E_0000h–0_000E_FFFFh
• System BIOS region; 64 KB area between 0_000F_0000h–0_000F_FFFFh.
The ISA expansion region is divided into eight 16 KB segments. Each segment can be assigned
one of four read/write states: read-only, write-only, read/write, or disabled. Typically, these blocks
are mapped through MCH and are subtractively decoded to ISA space.
The extended system BIOS region is divided into four 16 KB segments. Each segment can be
assigned independent read and write attributes so it can be mapped either to main system memory
or to the hub interface. Typically, this area is used for RAM or ROM.
The system BIOS region is a single 64 KB segment. This segment can be assigned read and write
attributes. It is by default (after reset) read/write disabled and cycles are forwarded to the hub
interface. By manipulating the read/write attributes, the MCH can “shadow” BIOS into system
memory.
4.1.3 ISA Hole Memory Space
BIOS software may optionally open a “window” between 15 MB and 16 MB (0_00F0_0000h to
0_00FF_FFFFh) that relays transactions to the hub interface instead of completing them with a
system memory access. This window is opened by programming the FDHC.HEN configuration
field.