Building a 4bit / 8bit computer in CPLD

8_Bit_Computer_by_Ben_AndersonSomething we’ve been working towards is building a homebrew CPU from scratch in CPLD. If you’ve seen any of our “Getting Started with CPLDs” guide, you might have noticed that we’re working towards completing the ALU before we can start adding proper CPU features to it. This article is less about the CPLD side of things (we’ll continue with the guides) and more about the rest of what we’ve been doing.

Building things on breadboards is fine but I often find that I either need to pinch something from the design, I knock wires out of place or there’s some other reason that it gets destroyed. In order to get round this, I’ve started building a modular control panel for my ongoing project. I’ve named it…. The Carlputer… ahem.

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Getting started with CPLDs – Part 8

cpldjIn this article, we’re going to re-use the hardware from the 4-bit binary adder but convert it into a 4-bit binary subtractor instead.

It’s a very simple modification to the schematic design. We simply invert the B inputs and leave the A inputs as they are. Instead of adding A and B, this configuration will subtract B from A.

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Getting started with CPLDs – Index

cpldjHere you will find links to all the articles that make up our CPLD for beginners guide.

We’d love to hear your feedback about this guide. If we’ve got something wrong or if there’s anything specific you’d like us to cover, please don’t hesitate to get in touch.

Part 1 – Installing the Altera Quartus II software
Part 2 – Entering your first design
Part 3 – Lighting an LED
Part 4 – Adding a button
Part 5 – Making a half-adder
Part 6 – Making a full-adder
Part 7 – Making a 4-bit binary adder
Part 8 – Making a 4-bit binary subtractor

 

 

 

Getting Started with CPLDs – Part 7

cpldjIn part 6, we built a 1-bit full adder. In this part we’re going to expand upon that and build a complete 4-bit binary adder. I have made the assumption that you already know about the binary number system but in case you don’t, have a look here and do some searching to learn about it.

Back? Great, let’s get on with it. Grab your CPLD development board, a breadboard and the usual handful of LED, switches and resistors. We will need switches for this guide instead of buttons.

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Getting Started with CPLDs – Part 4

cpldjIn this guide, we’re going to build up from the previous guide and add a button to our LED. Hopefully by now you’ve had a play with the Quartus II software and had a look through some of the logic elements in the library so I wont be explaining everything in minute detail. You should have a much better idea of what you’re doing now.

You’re going to need your CPLD board & programmer, a breadboard, LED, push button, 10K resistor, 220ohm resistor and some jumper wires.

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