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Welcome To The TTL CPU Website

This site is a collection of information about homebuilt/scratchbuilt computers. The main goal is to have a place to document my own attempts but it's just in its beginning stages so it's hard to say what the site will end up becoming.

The site was created Jan 10, 2012 so it's still pretty new and will evolve over time so feel free to poke around. I've added a series of pages under a section called My 4-Bit TTL CPU which follows my haphazard journey in building a scratch built TTL CPU. It's a very simple CPU but I'm sort of refining as I build and updating my notes as I build, test and learn more. The goal is to complete it and write some code to prove that it actually works.

Also check out the the links section. It has links to websites under several categories related to scratch built computers, electronics, theory, etc... I'll keep adding links as I go and intend to make it a one-stop links section for anyone who is the least bit interested in scratch built computer information. 

Anyway, poke around and enjoy!

New CPU Layout

Submitted by Andrew Wasson on Sun, 01/22/2012 - 12:25am

After I updated the Program Counter & Clock board the other day, I decided to rebuild the RAM board and add the board for the LED readouts so that I have one location for the Address, Instruction and Accumulator LED's. To do this I had to pull apart most of the work I had done previously which means I'm a little farther behind than I was a week ago. On the upside, because as I'm going through the cleanup I'm improving the wiring and installing decoupling caps so when It's finally done it should run glitch free.

New Clock and PC Board

Submitted by Andrew Wasson on Wed, 01/18/2012 - 6:58pm

Since I updated the site last week with the 4-bit Scratch Built CPU project, I decided to rebuild the board that holds the Clock, Program Counter, and improve the gates I'm using for my JUMP command. The improved board carries two 74LS161's (binary counters), a 74LS174 (upper 4 bit latch), a 74LS32 (NOR gate) and a 74LS132 (NAND Schmitt Trigger) and I'm using a 555 timer with a trim potentiometer for my adjustable clock generator.

My CPU Design

Submitted by Andrew Wasson on Thu, 01/12/2012 - 6:39pm

My CPU is a 4-bit RISC (reduced instruction set computer) design and has a maximum of 16 instructions. I chose a 4-bit CPU because it will be easier to troubleshoot than one with a wider datapath and the lessons I learn building this one can be built upon as I move to more complicated larger processors.

4-Bit TTL Scratchbuilt Computer

Submitted by Andrew Wasson on Wed, 01/11/2012 - 6:31pm

Image of 4-bit cpu wiring in progress
The 4-bit CPU about 75% wired (new photo Mar 18, 2012). It still needs a permanent clock, control wiring and microcode for the control section.

For as long as I can remember, I've been fascinated with computers and electronics. Some of my earliest memories include my grade 2 teacher reading a newspaper article about this university student who made a digital box called the 'Blue Box' to hack into the phone systems. His name was Steve Wozniac and four or five years later he would create the first Apple computer.


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