Homebrew CPU Plan Step 1

Ian Ward · November 5, 2021

Homebrew CPU Plan Step 1

This video introduces the first milestone for our homebrew CPU project.


The plan is to design a homebrew CPU just capable enough to build and play some basic games.

So to get started we’re going to use simple components to playback a sequence of commands to an LCD character display module.

First we’ll need something to store these commands then we’ll need some kind of counter to keep track of which command to send next and finally we’ll need a clock to advance that counter.

Our LCD display is a 20x4 display module powered by an HD44780 controller.

We can store more than 32 000 8-bit values with an AT28C256 EEPROM.

A 74LS163 binary counter stores a four bit value. Let’s use four of them to be able to count up to 32k.

A 555 timer will be our clock.

8-bit values from the EEPROM can be used to set the display module’s D0 through D7 inputs, but we’ll need to come up with a way to set the RS or “register select” input as well.

15 bits from our counter will drive the address pins of the EEPROM.

Our clock will drive the clock input to our counter but we’ll also need to generate a reset pulse to start the counter from the beginning, and feed back a halt signal to stop the clock when we reach the end.

I hope you’re interested in the project.

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