J041 SCPUB

Memory Map

The memory map can be altered by three options:

  1. on-board EPROMs are enabled by control latch bit 4 low
  2. on-board RAMs are enabled by control latch bit 5 low
  3. RAM size: 2k RAMs require LK5A open, and LK6B1 made.

Figure 10. Memory map

  Start End      
0K 0000






     3FFF
IC22 (16K) STEbus If on-board EPROM is disabled,
all accesses before 8000
are STEbus accesses.

If EPROMs smaller than 16K are used,
they will be echoed within the 16K space.

16K 4000






     7FFF
IC23 (16K)
32K 8000






     BFFF
STEbus
48K C000





     DFFF
IC20(8K) If on-board RAM is disabled,
all accesses after 8000
are STEbus accesses.
56K E000
     EFFF
Unused IC21(8K)
60K F000 F7FF IC20 (2K)
62K F800 FFFF IC21 (2K)

The address that is put on the bus during memory bus accesses is the same as the Z80 address: there is no translation. The Z80 address is 16 bits, however, and the STEbus address is 20 bits. The extra four bits come from the control latch, and these should be set to the correct value before the bus access is attempted.

Avoid switching memory from a program running in an area of memory that will be switched out, because the program will disappear as soon as the memory is switched!