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So I've designed this CPU with purely logical components (basic logic gates), now how would I go about converting it into a circuit? I know that logical gates can be implemented using transistors, but it seems pretty cumbersome to do the equivalent conversion for every gate (there are a couple hundred). In addition to this, adding the required resistors and other passive components due to physical constraints seems a bit cumbersome. Is there a secret to how this is generally done?

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the secret is that this is not generally done. you usually design your logic with a hardware description language, that already is a level of abstraction above logic gates, then some automatic tools (cost for enterprise > 10k$) translates the code in masks that are used to produce the chip. sometimes, for prototyping, an FPGA is used: that's a bunch of gates with programmable interconnections. The question is: what piece of sw did you use for your design? –  Vladimir Cravero Aug 7 at 9:52
@VladimirCravero, is that really how it is done in industry? I knew FPGAs were used for prototyping a new device, but would someone like Intel or AMD program their new CPU design in VHDL, have software create some FPGA-like minimal design (with only the necessary used internconnections) and then send it to the fab? –  sherrellbc Aug 7 at 12:15
Yes, it would be done in VHDL or Verilog. The layout to individual logic gates is then mostly automatic, with a bit of hand-tuning of timing critical parts. Placed logic gates -> production masks is one of the conceptually simpler parts of the process. –  pjc50 Aug 7 at 12:29

3 Answers 3

up vote 8 down vote accepted

For practical purposes of getting it working on your desk, you probably want an FPGA.

In order to make sure it works, you should simulate it first with a program like Modelsim. This enables you to iron out the bugs before buying any hardware.

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Texas Instruments, et al. have almost unbelievably extensive stables of digital logic functions available which can be assembled into pretty much anything you want.

Go here and here , then check out HC (HCMOS) to get started.

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While the above answers are correct, in the late 70's through the early 90's sometimes simple CPU's were constructed from TTL logic. While you may or may not want to get into such a project, it is interesting concept. Because the CPU is spread out and hand wired you can probe around and see it in its entirety rather than just as a small black box.

Here's one that I found that is along the lines of what I've seen in the past:

4-Bit TTL Scratchbuilt Computer

Here's another that I think would be a mess to debug but still fun to work on:

Instructables - How to Build an 8-Bit Computer

Good luck with whatever you choose.

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