[geeks] Crackpot project, need some guidance

[Mouse]

[I was going to send this offlist, but then I read the headers and
noticed you send through google and thus can't write me directly.]

> I have a working 16-bit ALU but I am struggling to see the 'bigger
> picture' as far as integrating the instruction set with the ALU and
> registers and memories.

Thinking of it in terms of data flow might help.  If you have a value
that needs to get from, say, memory to the ALU for some instruction,
then add decoding logic so that, for that instruction, a signal is
generated that gates memory data onto that ALU input.

If you look at instruction sets, especially of simple CPUs like the
8080, you'll see a lot of commonalities, such as "all the instructions
that read from memory have the same bits in these positions".  This is
done because it simplifies that decoding logic.

If you're building a microcoded CPU, you might consider a
non-microcoded machine as your first attempt - or, to put it another
way, let your "machine code" be microcode.  Basically, "start simple".

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