Description for CS/A KEYEMU, version 1.0
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whatsit : 6502 Emulation board
I/O     : 2*256 byte `dual-ported' RAM at $c** and $d**
Mem     : --

This board provides two pages of 256 byte pseudo-dual-ported RAM.
Two connectors provide (each) 8 address line inputs and 8 data line
outputs. The connectors can only read the RAM. After providing
the address the data lines become valid at least 2 CS/A65 bus cycles
after that. 

The onboard memory is time-shared between the CS/A CPU and the two 
connectors (Phi2 high: CPU, Phi2 low: connectors). The data for one 
of them is read the one cycle, the others connectors data in the next 
cycle and so on.

As long as no special keyboard scan routine is used, this board can 
be used to simulate the keyboard of a C64, or of a PET.
In case of the C64 the valid scan data must be put at addresses
$fe, $fd, $fb, $f7, $ef, $df, $bf, $7f.
For the PET the keyboard lines before the 4-to-10 decoder can be used
and the valid codes can then be written to addresses $0-$9

The pinout of the keyboard connectors is arbitrary. I have built a small
keyboard adaptor for the C64 to attach a flat cable with 20 lines.
The pinout of the connectors represents this cable pinout.