The art of digital design

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1. rahenJun 2022
   To be pedantic, the 6502 is luxury compared to the PDP-8. It has twice the number of instructions, more registers, and... a stack. Without a stack, Digital used a convoluted trick to implement their subroutines. They would store the current PC address at memory location 0, branch to the subroutine, then branch back to the address referenced at location 0 when the routine was done.

   Then we have the EE implementation. Digital came up with all the tricks in the book to save components: wired OR gates, gates that act as NAND or NOR depending on the input voltage, diode-capacitor gates and more.

   The "straight" 8 is an EE marvel. Without any extension such as floating point arithmetic, they managed to engineer its logic in DTL using an outstandingly low count of 1409 transistors. I don't think anything has ever come close to that. In comparison, a 6502 requires around 3500, more than twice the straight 8.

   And the PDP-8 could use multiple disk storage and teletypes at the same time, drive lab equipment, run an OS, have several users... it was quite more versatile and useful than 6502 8-bit computers.

   This makes the PDP-8 one of the more interesting computer architecture to study, and indeed it has been used as a reference in many EE books. In particular, check out "The Art of Digital Design", Prosser, 2nd edition, which re-creates one in TTL logic.

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2. TruffleLabsApr 2025
   Art of Digital Design: An Introduction to Top-Down Design - Prosser & Winkel, I took their graduate class in 1990 at IU Bloomington.

   In this class I & my lab partner designed and built a PDP-8 out of PALs on a wire wrapped board. And we loaded code from old paper tape sources as part of the testing. It was a fun class :)

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3. nxobjectSep 2024
   Just to add a few more resources – ye olde digital design books are really fun to learn how (sequenced) microcoding was seen as one of the highest-level tools in the toolkit of digital design in general up to the early/mid 80s:

   – "Computation Structures", an old MIT course book, which uses a pedagogical processor similar to a microcoded PDP-11 or a 68k, to illustrate microcoding as the highest level of digital design – the processor they implement used a two-level microcoded processor to implement two types of processor on the same microcode interpreter engine, complete with built-in monitor/debugger.

   – "The Art of Digital Design", an older course text, which culminates in the implementation of a PDP-8 clone;

   Finally, if it helps look up more literature, another name for microprogramming in the literature is "interpretive microcoding" – one that makes the distinction between ye olde microprogramming and modern "microoperations" pretty clear.

   It also clarifies why two-level micro-coding might exist, especially in the microarchitecture of the original 68k: you write in high-level microcode an engine interpreting a target ISA; this high-level microcode interpreter is then interpreted by low-level microcode that directly activates control lines. Two levels of interpretation seems baroque, but somehow it was fast enough for 68k workstations.

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4. cptnapalmJun 2022
   There is a much older text book called the Art of Digital Design. In it, if you buy and solder the necessary components, you get a fully working PDP-8.
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5. cptnapalmJun 2020
   I've tried a few times to get started learning, but I always hit serious snags. I've tried Practical Electronics for Inventors, but got lost in all the electrons. I got decently far in Art of Digital Design (culminates in making a PDP-8) but hit a part too hard for me and got stuck. Any suggestions?
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6. kaysonJun 2020
   For a practical understanding of electronics, there's no need to go so far deep into the theory that you'd get "lost in all the electrons". I really like HyperPhysics for the basic, basic theory - http://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#emcon I would go through the Circuit Elements tree first, then the Electric Circuits. If you want to go further, there are tons of college courses with lecture notes available online. You're probably looking for something like an EE201/Electronic Circuits. Here's one I found that seemed to have all the important topics: http://tuttle.merc.iastate.edu/ee201/topics.htm Unfortunately, sometimes the lecture notes are hard to understand since they're not meant to be a standalone tutorial. You may also check MIT or Stanford for their free course versions, which probably have the entire lecture.

   From there, to be honest, I'm not sure what to suggest. One thing I usually recommend to people interested in electronics is to pick up a breadboard kit/tutorial like one by Elegoo on Amazon. It's slightly more programming focused, but it covers a lot of other circuit topics and it's a great way to get started with experimentation. I find that being able to actually produce something as you're learning makes it a lot more engaging.

   Art of Digital design is a 2nd or 3rd year college level textbook so you might be missing some context there. I would say if you want to go further, look into a transistor-level circuit course (which I took after EE201). That covered both analog and digital transistor circuits, which supported the digital design class I was taking at the same time.

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