Specifications

EPC-21/22 Hardware Reference
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For systems with 1 Mbyte of base memory, the memory technology is 4Mbit chips
organized as two 256K by 18-bit banks. This base memory configuration can be
identified on the board by examining the memory chips and the corresponding pads.
The circuit board provides 42 pads per chip but the chips are 40-pin. Therefore the
rear-most pads are not used.
For systems with 4 MBytes of base memory, the memory technology is 16Mbit chips
organized as two 1MB x 18-bit banks. As with the 1 MByte system, identifying this
memory configuration requires looking closely at the rear pads at location U12 and/or
U13. All pads are used for this memory configuration.
Memory Expansion
In addition to the base memory, a single 72-pin SIMM socket is provided for memory
expansion. SIMM memory occupies banks 2 and 3. Any standard SIMM module
may be used that meets the following criteria:
- fast page mode
- 72-pin
- 80 nanosecond DRAM
- single-sided
- one- or two-bank
Allowable system memory configurations and the specifics of which SIMM to use
are dependent on the system base memory. The tables below specify the correct
SIMM module for each possible configuration.
For 1 Mbyte of base memory
Total
Memory
SIMM
Memory SIMM organization
1 MB None
3 MB 2 MB 1 bank 1 MB x 18-bit
5 MB 4 MB 2 banks 1 MB x 18-bit
9 MB 8 MB 1 bank 4 MB x 18-bit