20xt6 Homebrew CPU Project

Homebrew CPU Plan Step 1

Homebrew CPU Plan Step 1

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

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Simple Clock Circuit with a 555 Timer

Simple Clock Circuit with a 555 Timer

In this video we create a clock circuit with a 555 timer in astable mode, and use it to blink a green LED.

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Manual Clock Circuit Controls

Manual Clock Circuit Controls

We add a potentiometer and a single-step button to our clock circuit.

schematic & transcript

Synchronous 4-bit Binary Counter 74LS163

Synchronous 4-bit Binary Counter 74LS163

We connect our clock circuit to a 74LS163 synchronous binary counter and see how to count, reset and load values into the counter.

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16-bit Address Register

16-bit Address Register

We add three more 74LS163’s to our counter to make a 16-bit address register for our homebrew CPU project.

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Power-on and Manual Reset Circuit

Power-on and Manual Reset Circuit

We add a reset circuit to our clock module that resets our address register to “0” on power-on and when a button is pressed.

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Clock Halt Circuit with 4011 NAND Gate and 555 Timer

Clock Halt Circuit with 4011 NAND Gate and 555 Timer

We complete our clock module by adding a halt signal and test it with our address register. Now our (future) programs won’t have to run forever.

schematic & transcript

SST39SF040 512k Flash Upgrade

SST39SF040 512k Flash Upgrade

We build a larger address register and use it to test an SST39SF040 512k flash chip.

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Milestone 1: LCD Character Display

LCD Character Display

We connect an HD44780-powered LCD character display to the circuit and play a simple text animation from the program ROM.

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CMOS vs TTL: What are logic families?

Replaced 4011 with 7400

In this video we replace our clock’s 4011 CMOS Quad-NAND gate IC with a TTL equivalent and discuss compatibility between different logic families.

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