Memory expansion for P5 rev2

Here’s another project I’ve been figuring for some time turning something real. One of the limitations of the rev2 has been small 128 byte memory which has is more or less totally used specially with the upgraded firmware.

Here’s a 2k expansion board which replaces the 60B10 memory on board. The SPRAM is now expanded to 1k and second 1k is used for patch memory upgrade.

The bank select runs from 00 to 98, 51-98 can be selected between expanded memory or factory patches.

Expansion sits piggybacked on rom2 socket and two pins are inserted where the removed 68B10 was. Extra wires carry battery supply and /ce -signal.