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Processor Configuration Registers 
 
 
 
14  
 
Datasheet  
Compatible SMRAM Address Range (A_0000h-B_FFFFh) 
When compatible SMM space is enabled, SMM-mode CPU accesses to this range are 
routed to physical system DRAM at 000A 0000h - 000B FFFFh. Non-SMM-mode CPU 
accesses to this range are considered to be to the Video Buffer Area as described 
above. DMI originated cycles to enable SMM space are not allowed and are considered 
to be to the Video Buffer Area if IGD is not enabled as the VGA device.  
Monochrome Adapter (MDA) Range (B_0000h-B_7FFFh) 
Legacy support requires the ability to have a second graphics controller 
(monochrome) in the system. Accesses in the standard VGA range are forwarded to 
IGD or the DMI Interface (depending on configuration bits). Since the monochrome 
adapter may be mapped to anyone of these devices, the IMC must decode cycles in 
the MDA range (000B_0000h - 000B_7FFFh) and forward either to IGD or the DMI 
Interface. This capability is controlled by a VGA steering bits. In addition to the 
memory range B0000h to B7FFFh, the IMC decodes IO cycles at 3B4h, 3B5h, 3B8h, 
3B9h, 3BAh and 3BFh and forwards them to the either IGD and/or the DMI Interface. 
1.2.1.3 
Expansion Area (C_0000h-D_FFFFh) 
This 128 KByte ISA Expansion region (000C_0000h – 000D_FFFFh) 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 IMC and are subtractive decoded to ISA space. Memory that is disabled is not 
remapped.  
Non-snooped accesses from DMI to this region are always sent to DRAM. This 
complies with a Colusa DCN. 
Table 1-1. Expansion Area Memory Segments 
Memory Segments 
Attributes 
Comments 
0C0000H  
WE  RE 
Add-on BIOS 
0C4000H  
WE  RE 
Add-on BIOS 
0C8000H  
WE  RE 
Add-on BIOS 
0CC000H  
WE  RE 
Add-on BIOS  
0D0000H  
WE  RE 
Add-on BIOS 
0D4000H  
WE  RE 
Add-on BIOS 
0D8000H  
WE  RE 
Add-on BIOS 
0DC000H  
WE  RE 
Add-on BIOS 
1.2.1.4 
Extended System BIOS Area (E_0000h-E_FFFFh) 
This 64 KByte area (000E_0000h – 000E_FFFFh) is divided into four 16 KByte 
segments. Each segment can be assigned independent read and write attributes so it 
can be mapped either to main DRAM or to DMI Interface. Typically, this area is used 
for RAM or ROM. Memory segments that are disabled are not remapped elsewhere.