> Then LogicSim got a bit slow and we switched to LogiSim (no "c") and 
> are
> just about ready to put together a minimal 4 bit uC with a program 
> memory,
> program counter, source and destination decoders, ALU, accumulator, 
> input
> and output.

If you haven't got a firm architecture in mind have a look at the 
PDP-8 instruction set to see what you can do with very little. 8 
instructions :-). Note the reason that the ADD is names TAD (or was 
that TADD?). The subroutine return method is a bit "non standard" by 
today's standards but made sense at the time. [[The preceding from 
memory, and I never actually used one so E&OE]].



            Russell. 

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