Specifications

EPC-33/34 Hardware Reference
Page 28
3 3
Memory
The EPC-33/34 supports one bank (a bank is a single- or double-sided SIMM) of
70ns fast page mode DRAM installed in a 72 pin SIMM socket. The SIMM parts
used on the EPC-33/34 are 3.3 volt versions of sizes 1Mx32 (4MB), 2Mx32 (8MB),
4Mx32 (16MB) and 8Mx32 (32MB). The EPC-33/34 does not use parity DRAM.
After power on reset, the BIOS finds and sizes the memory present in the system.
The DRAM timing (in CPU clocks) in the EPC-33/34 system is set to enable the
80486 bus to achieve 4-2-2-2 timing. The EPC-33 can use SIMMs with speeds down
to 80ns due to the slower bus clock speed.
The DRAM controller is set to map 80486 addresses in the region from 0x000C8000
to 0x000EFFFF to the AT-bus. The area from 0x000C8FFF to 0x000DFFFF may be
used as shadow areas configured through setup. Memory accesses beyond the
installed DRAM and not overlapping the 1MB video memory at 0x2000000 to
0x20FFFFF are automatically sent to the AT-bus. The video memory is above the
system memory.
To improve the performance of the BIOS that is initially contained in an 8-bit wide
Flash EPROM, the BIOS is shadowed in the DRAM at address 0x000FXXXX after
power-on reset. The VGA BIOS is shadowed in the region 0x000C0000 to
0x000C7FFF.
Memory Expansion
A single 72-pin SIMM socket is provided for memory expansion. Modules must
meet the following criteria:
- fast page mode, non-parity
- 72-pin, 3.3V
- 70 nanosecond DRAM or faster
Recommended part numbers for SIMMs are discussed in Chapter 6, Upgrades.