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CM1-86DX3
Appendix A System Resources
This appendix provides system resource specifications for the CM1-86DX3 including Memory
addresses, IO addresses, PCI configuration registers, IO registers, and system interrupts.
A.1 Memory Address Map
The SoC supports 4 GBytes of addressable memory space and 64 KBytes of addressable I/O
space. In order to be compatible with a PC/AT system, the lower 1 MBytes of this addressable
memory is divided into regions which can be individually controlled with programmable attri-
butes such as disable, read/write, write only, or read only.
Figure 2 represents the SoC memory address map. It shows the main memory regions
defined and supported by the SoC. At the highest level, the address space is divided into
two main conceptual regions. One is the 0-1-Mbyte DOS Compatibility region, and the
other is the 1-Mbyte to 4-GByte Extended Memory region.
DOS Compatibility Region
The first region of memory is called the DOS Compatibility Region and it was defined for early
PCs.This area is divided into the following address regions:
X
0-640 KByte DOS Area
X
640-768 KByte Video Buffer Area
X
768-896 KByte in 16 KByte section (total of 8 section)-Expansion Area
X
896-960 KByte in 16 KByte section (total of 4 section)-Expansion System BIOS Area
X
960 KByte-1Mbyte Memory (BIOS Area)-System BIOS Area
DOS Area (00000-9FFFFFh)
The DOS area (0000H-9FFFFh) is 640 KBytes in Size. It is mapped to the main memory con-
trolled by the SoC.
Video Buffer Area (A0000-BFFFFh)
The 128 KByte graphics adapter memory region is normally mapped to a video device on the
PCI bus (Typically VGA controller). This area is controlled by the A/B Page control Register. It
can be mapped to either the main DRAM or the PCI bus for both read and write commands.
ISA Expansion Area (C0000–DFFFFh)
This 128-KByte ISA Expansion region is divided into eight 16-KByte 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 the PCI bridge to ISA space. Memory that is dis-
abled is not remapped.
Extended System BIOS (E0000–EFFFFh)
This 64-KByte area is divided into four 16-KByte segments. Each segment can be assigned
independent read and write attributes so it can be mapped either to the main DRAM or to the
PCI bus. Typically, this area is used for RAM or ROM. Memory that is disabled is not remapped.
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