CSCvon8: An 8-bit TTL CPU

This is an 8-bit CPU built using only 17 TTL chips. 32K ROM, 32K data, UART, microcoded.

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This is about as minimal as you can get for a von Neumann style 8-bit CPU made from TTL chips. The project contains the hardware design, a Perl and a Verilog simulator, an assembler, a compiler and over a dozen example programs including Conway's Game of Life and a Tic Tac Toe program. Full details of the project are at

A while back I saw Ben Eater's great video series on building a computer from gates. I wondered how few 7400-series chips were needed to build something useful, and I created the 4-bit CSCv2 computer:

With this project I've taken the same goal, a minimum number of 7400-series chips, and built an 8-bit computer with 64K of address space. This time I've fabricated a PCB for the project and got it running at 3.57MHz. If you would like more details of the CPU's architecture, there is a design document here:

I've also written a long set of notes on how to build the CPU here:


All CSCvon8 files are available at

plain - 73.00 bytes - 06/07/2019 at 09:58


  • 1 × AS6C62256 Memory ICs / Static RAM (SRAM)
  • 1 × 28C256 Memory ICs / PROMs, OTP PROMs
  • 1 × AT27C1024-70PU Memory ICs / PROMs, OTP PROMs
  • 1 × 74HCT139 Electronic Components / Misc. Electronic Components
  • 1 × 74HCT138 Electronic Components / Misc. Electronic Components

View all 12 components

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kaimac wrote 07/16/2022 at 13:49 point

Great project - your notes on timing have been very helpful. I'm wondering how it can run at 3.5 MHz given the propagation delays you listed - i.e. 242 ns to decode a microinstruction and fetch a value from ROM - but this would need to be done within one half cycle (140 ns), wouldn't it?

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George Tyler wrote 06/28/2019 at 03:54 point

I once had a job working with a computer made out of 74 series logic chips, cpu  was 32 bits, 1 bit per pcb card. Memory was 32k magnetic core memory. It ran at 20mhz, but they had to match chips to get signals arriving at the same time! also some lines has extra gates that seemed to do nothing, there for the delay. It did a LOT!  26 coding desks with keyboards, many motors, sensors and flaps that controlled how letters were directed. program and data loaded from paper tape. (teletype) Amazing training! 

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Ken Yap wrote 06/23/2019 at 12:14 point

Congrats. I see you've done this substitute computation by lookup time space tradeoff before. :)

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