Comments: Digital Logic


Comments 9 comments

  • Truth Tables. The engineer’s Punnett Squares.

  • Isn’t XNOR also one?? :)

    • Yes, strictly speaking, it is. But it’s so rarely used as a concept that it doesn’t really bear mentioning.

      Which is interesting, considering that the base circuit most easily achieved is, in fact, an XNOR gate, much as the base circuits are NAND and NOR. To get an XOR (or AND or OR) we have to invert the output of the corresponding base circuit, at a cost of two extra transistors.

  • This is exactly what I’ve been looking for. For years. This is where I should’ve come before learning to program.

  • The sequential logic is interesting to me, but I don’t know what Q in the diagrams stands for. Pretty basic I expect, but hard to follow without it.

    • Q is the output of a register, and Qbar is the inverse output of Q. Q doesn’t really stand for anything, but is generally accepted as the state output of the flip-flop.

      There are a lot of theories and speculation on why Q was used, but the best answer I like refers back to Turing and his machine. Since digital logic is discrete in nature (not continuous because it depends on state), it refers to the quanta, or state at the time specified.

  • Great tutorial, but a few things you should add to it.

    1. K-maps. You have Q-M algorithms, which is advanced stuff, K-maps are way easier to do and mostly taught in colleges.
    2. No mention of CPLDs/FPGAs in additional resources (this is where most digital logic work is done nowadays).
    3. Additional resources should have HDL resources.
    • We’ll actually probably cover HDL and CPLD/FPGA stuff in another tutorial.

      As for the K-map thing, I gave some thought to K-map vs. QM and felt like K-map requires a little more intuitive sense (in terms of heuristics) and QM is basically a “turn-the-crank” type operation. I’ve wondered how others would feel about that…I may add K-maps to the tutorial later on.

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