Specifications

Chapter 5: Theory of Operation
Page 49
55
Memory Map
The 2
32
byte physical address space seen by the Intel486 occupies three areas:
1. Addresses between 0 and 1 MB, which are largely defined by the IBM
PC/AT architecture.
2. Addresses between 1 MB and 256 MB, which largely depend on how
much DRAM is installed in the EPC-5A.
3. Addresses above 256 MB, which provide direct mapping to the VMEbus
with a variety of address modifiers and byte orderings. See Chapter 6,
The VMEbus Interface, for more information about this feature.
Memory at addresses between 0 and 1 MB (0FFFFFh) is mapped as follows:
Range Content
000000 - 09FFFF DRAM (first 640 KB)
0A0000- 0BFFFF Mapped to EXM interface; almost always used by a
video controller as video RAM
0C0000 - 0C7FFF Write-protected DRAM containing video BIOS
0C8000 - 0DFFFF* Uncommitted; mapped to EXM interface
0E0000 - 0EFFFF User-mappable hardware window onto VMEbus
0F0000 - 0FFFFF Write-protected DRAM containing BIOS
* 0C8000 - 0DFFFF may be used either as page frames (i.e. for Ethernet, etc.) or
may be used by DOS as upper memory blocks if an EMM driver is installed or
may be used for BIOS extensions.
For a 4 MB EPC-5A, the extended memory address space is defined as
00100000 003FFFFF 3 MB DRAM extended memory
00400000 00FEFFFF Uncommitted; mapped to EXM interface
For an 8 MB EPC-5A, the extended memory address space is defined as
00100000 007FFFFF 7 MB DRAM extended memory
00800000 00FEFFFF Uncommitted; mapped to EXM interface
For a 16 MB EPC-5A, the extended memory address space is defined as
00100000 00FFFFFF 16384 KB DRAM extended memory