J131 SCPC88 Processor Board Manual
The EPROM sizes are set by LK6-9, and can be from 16K (27128) to 64K (27512). The 256K DRAM is selected by the signal /CAS. Wait-states are not produced for on-board memory. DRAMs with access times shorter than 210 ns, and ROMs faster than 250 ns will run up to 7.16 MHz).
If a memory access is made to an address which is within neither on-board RAM or ROM, the STEbus will be selected automatically. This may result in a bus timeout if no actual memory exists on the bus.
00000 3FFFF |
256K onboard DRAM (fitted as standard) | |
40000 | PC RAM expansion area (up to 640K maximum) | STEbus accesses |
A0000 BFFF |
EGA Screen RAM | |
C0000 C3FFF | SPEGA BIOS ROM | |
D0000 DFFFF |
||
E0000 EFFFF |
SCPC88 onboard expansion EPROM | |
F0000 FFFFF |
SCPC88 onboard BIOS EPROM (64K reserved area) |