5 ms·

Instruction fetcher + address lines and how these things are wired together. If you are really interested, there are various people having big sets of videos ab

Instruction fetcher + address lines and how these things are wired together. If you are really interested, there are various people having big sets of videos about creating an 8 bit CPU from scratch with TTL logic chips. Alternatively, or on top of that, you can dig up reference / hardware manuals about relatively simple CPUs / SoCs and look at the initialization parts and pieces.

MichaelZuo 3y ago
Thanks for the info, though I think the point where I'm curious about is how exactly the 'TTL logic chip' itself starts-up. Are there any 'how-to-make TTL logic chips from scratch' resources that you know of? For example, the die images and schematic of the most basic TTL chip, the SN7400: https://en.wikipedia.org/wiki/File:SN7400_1965.jpg https://en.wikipedia.org/wiki/File:SN7400_1965.jpg https://en.wikipedia.org/wiki/File:TTL-00-die-schema.jpg https://en.wikipedia.org/wiki/File:TTL-00-die-schema.jpg Show odd patterns and I can't figure out how pushing electricity across it will make it do anything other than heat up.
- pixelfarmer 3y ago
  Sorry for the late reply! What you see on these dies can also be recreated manually with transistors, diodes, resistors, and maybe the odd capacitor. https://en.wikipedia.org/wiki/7400-series_integrated_circuits https://en.wikipedia.org/wiki/7400-series_integrated_circuit... shows further down the on die circuit. There is https://en.wikipedia.org/wiki/NAND_gate https://en.wikipedia.org/wiki/NAND_gate to give you further examples, plus there are links to TTL logic in general and all sorts of other gates. It should be easy to find pages that show how to recreate this stuff with actual transistors and resistors (or youtube videos for that matter). The startup is pretty much just powering these chips and maybe having the input lines defaulting to for example "low" with resistors for a defined input and then output state (if the chips don't offer that themselves already -> chip manual). However, all that doesn't happen in zero time, same as signal propagation which needs time, but this is also part of such chip manuals to tell you about the timings, max frequencies etc. they can be operated at.
  - MichaelZuo 3y ago
    > It should be easy to find pages that show how to recreate this stuff with actual transistors and resistors (or youtube videos for that matter). Well I haven't found any, even a how-to guide on linking together the gates on a breadboard and getting it to perform any operation that a TTL performs is way beyond the literature I've seen on the internet. Do you know of some reference source?
    - pixelfarmer 3y ago
      Something like that? https://www.dummies.com/article/technology/electronics/circuitry/electronics-projects-how-to-create-a-transistor-nand-gate-circuit-179366/ https://www.dummies.com/article/technology/electronics/circu... or https://www.youtube.com/watch?v=sTu3LwpF6XI https://www.youtube.com/watch?v=sTu3LwpF6XI and there are truckloads more of these. There used to be electronics sets for kids with breadboards (some of them larger scale for easier physical handling then standard breadboards), and they'd had manuals with them explaining all the things. I remember that they also contained descriptions of basic gates like (N)AND, (N)OR, NOT, plus flip flops for storing 1 bit of data.
      - MichaelZuo 3y ago
        These all seem much simpler then replicating the real world functionality of even the simplest TTL chips. There's a huge gap between making a single gate or a few gates, and making something even as basic as the SN7400 from 1965. I don't think I'm the first person in history to have noticed this, but the lack of learning materials is very odd.
        pixelfarmer 3y ago
        Yes, because these chips follow certain design goals the simple examples don't care about. For example, assume you start scaling things up, there is the problem of "load" (aka current). If you look at the chip manuals you will see how much current the inputs require to work, you will see how much max. current the outputs are able to handle, and now imagine you have to wire many of these chips together or drive other stuff with it. This is why for example for LEDs you may need an additional transistor or even a driver IC (for multiple LEDs) to get the LEDs working, because the chip itself is not able to handle the current load. There are things like switching frequencies, current load related stable output voltages which may require replacing passive elements (e.g. resistor) with active ones (diode / transistor), and so on. Read: This goes far beyond the core gate functionality to actually have something usable in a wide range of applications.

MichaelZuo 3y ago

Thanks for the info, though I think the point where I'm curious about is how exactly the 'TTL logic chip' itself starts-up. Are there any 'how-to-make TTL logic chips from scratch' resources that you know of? For example, the die images and schematic of the most basic TTL chip, the SN7400: https://en.wikipedia.org/wiki/File:SN7400_1965.jpg https://en.wikipedia.org/wiki/File:SN7400_1965.jpg https://en.wikipedia.org/wiki/File:TTL-00-die-schema.jpg https://en.wikipedia.org/wiki/File:TTL-00-die-schema.jpg Show odd patterns and I can't figure out how pushing electricity across it will make it do anything other than heat up.

pixelfarmer 3y ago
Sorry for the late reply! What you see on these dies can also be recreated manually with transistors, diodes, resistors, and maybe the odd capacitor. https://en.wikipedia.org/wiki/7400-series_integrated_circuits https://en.wikipedia.org/wiki/7400-series_integrated_circuit... shows further down the on die circuit. There is https://en.wikipedia.org/wiki/NAND_gate https://en.wikipedia.org/wiki/NAND_gate to give you further examples, plus there are links to TTL logic in general and all sorts of other gates. It should be easy to find pages that show how to recreate this stuff with actual transistors and resistors (or youtube videos for that matter). The startup is pretty much just powering these chips and maybe having the input lines defaulting to for example "low" with resistors for a defined input and then output state (if the chips don't offer that themselves already -> chip manual). However, all that doesn't happen in zero time, same as signal propagation which needs time, but this is also part of such chip manuals to tell you about the timings, max frequencies etc. they can be operated at.
- MichaelZuo 3y ago
  > It should be easy to find pages that show how to recreate this stuff with actual transistors and resistors (or youtube videos for that matter). Well I haven't found any, even a how-to guide on linking together the gates on a breadboard and getting it to perform any operation that a TTL performs is way beyond the literature I've seen on the internet. Do you know of some reference source?
  - pixelfarmer 3y ago
    Something like that? https://www.dummies.com/article/technology/electronics/circuitry/electronics-projects-how-to-create-a-transistor-nand-gate-circuit-179366/ https://www.dummies.com/article/technology/electronics/circu... or https://www.youtube.com/watch?v=sTu3LwpF6XI https://www.youtube.com/watch?v=sTu3LwpF6XI and there are truckloads more of these. There used to be electronics sets for kids with breadboards (some of them larger scale for easier physical handling then standard breadboards), and they'd had manuals with them explaining all the things. I remember that they also contained descriptions of basic gates like (N)AND, (N)OR, NOT, plus flip flops for storing 1 bit of data.
    - MichaelZuo 3y ago
      These all seem much simpler then replicating the real world functionality of even the simplest TTL chips. There's a huge gap between making a single gate or a few gates, and making something even as basic as the SN7400 from 1965. I don't think I'm the first person in history to have noticed this, but the lack of learning materials is very odd.
      - pixelfarmer 3y ago
        Yes, because these chips follow certain design goals the simple examples don't care about. For example, assume you start scaling things up, there is the problem of "load" (aka current). If you look at the chip manuals you will see how much current the inputs require to work, you will see how much max. current the outputs are able to handle, and now imagine you have to wire many of these chips together or drive other stuff with it. This is why for example for LEDs you may need an additional transistor or even a driver IC (for multiple LEDs) to get the LEDs working, because the chip itself is not able to handle the current load. There are things like switching frequencies, current load related stable output voltages which may require replacing passive elements (e.g. resistor) with active ones (diode / transistor), and so on. Read: This goes far beyond the core gate functionality to actually have something usable in a wide range of applications.