This reminds me so much of a homework problem in our microprocessors class (ca. 1982) - using discrete logic (no microcode lookup tables). We did have bit shifts, adders (including increment/decrement), AND/OR/NOT/XOR/XAND logic, branch and loop instructions - 63 instructions in all. It was a simplified version of the Intel Prompt-80s (8080 based) in our lab, and we were to use what we built for the rest of the semester and not the Intel or Motorola boxes. Note that addressing was linear (not segmented) and registers were little-endian like Motorola, not big-endian like Intel.
-- Scott G. Hall Raleigh, NC, USA [email protected] *”**Failure is the opportunity to begin again more intelligently.” -- Henry Ford* On Mon, Jun 22, 2026, 11:27 AM John Wettroth via TriEmbed < [email protected]> wrote: > That’s pretty amazing. It’s pretty functional overall with a few quirks > (see below). I always wanted to do something like this. This is one of > the cleaner designs like this I’ve seen. I like that’s it pure logic vs > being table based/micro coded. > > One of the fun things about designing a CPU is that you get to design the > perfect instruction set. This instruction set is 4 bits wide- 16 > instructions, this keeps it simple for direct logic implementation > > > > A few things to note- > > It’s a Harvard type architecture- data and address busses are 8 bits. > > No subroutines, no indirect addressing of rom or ram > > There are no logical operations- and/or/xor etc.- some of these I guess > you could fake with add and subtract which are present. > > There is no inc or dec instructions > > There are also no shift instructions, I’m a bit twiddling microcontroller > guy, I need shifts. > > > > There is a Halt and a NOP instruction. A halt is kind of a nice > instruction for a proto computer but NOP can almost always be faked- i.e. > MOV A,A > > > > One of the coolest baby architectures that I’ve seen is the RPi Pico PIO. > They made different compromises but it is so functional for how tiny it is. > > > > This might be the deepest rabbit hole that you can bury yourself in, looks > like fun. > > > > Thanks for sharing! > > > > Regards, > John M. Wettroth > > E: [email protected] > M: (919) 349-9875 > H: (984) 329-5420 > > > > *From:* TriEmbed <[email protected]> *On Behalf Of *Pete > Soper via TriEmbed > *Sent:* Sunday, June 21, 2026 1:45 PM > *To:* Triangle Embedded Interest Group <[email protected]> > *Subject:* [TriEmbed] A more interesting 8 bit processor > > > > This is both a simulation and a hardware design using easy to understand > logic chips: > https://github.com/c0rRupT9/STEPLA-1 > _______________________________________________ > Triangle, NC Embedded Interest Group mailing list > > To post message: [email protected] > List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org > TriEmbed web site: https://TriEmbed.org > To unsubscribe, click link and send a blank message: mailto: > [email protected]?subject=unsubscribe > Searchable email archive available at > https://www.mail-archive.com/[email protected]/ > >
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