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LEO-1 Homebrew CPU

16-bit computer system featuring a custom-designed CPU

john-croudyJohn Croudy
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The LEO-1 is a complete 16-bit computer system featuring a custom-designed CPU. The project has been in progress (on and off) since May 2015. Main features:

- 16 bit data bus.
- 24 bit address bus (16 megaword address space).
- Custom CPU with RISC instruction set (no microcode).
- Mostly built from 74HC series integrated circuits.
- Four tier design - ALU board, Register board, Control board, Memory & devices board.
- 640 kilowords of ROM, 3 megawords of RAM.
- Fast and slow modes with single step facility.
- Target clock speed was 1MHz in fast mode. It actually works reliably at 4MHz.
- Most important signals and buses displayed on 256 front panels LEDs.
- Integrated VDU card with monochrome character graphics (40 width/height modes).
- Real Time Clock and DIP switch devices.
- Four expansion ports for external devices, IDE and general-purpose I/O.
- Expansion devices should include thermal receipt printer and custom keyboard.

Details can be found here:

http://puntett.net/leo1cpu/main.htm

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John Croudy wrote 02/18/2018 at 21:44 • point

Here are a few videos:

https://youtu.be/ftok5QBDIvo

https://youtu.be/pBxxLNo1fCM

  Are you sure? yes | no

Marcel van Kervinck wrote 02/18/2018 at 21:57 • point

Isn't that fantastic, thanks for showing!

  Are you sure? yes | no

Yann Guidon / YGDES wrote 11/15/2019 at 16:19 • point

The videos are not available anymore :-(

  Are you sure? yes | no

John Croudy wrote 11/16/2019 at 01:01 • point

Thanks for pointing this out. I reorganized my videos a while ago and I must have made a mistake. I'll sort it out tomorrow.

  Are you sure? yes | no

Yann Guidon / YGDES wrote 11/16/2019 at 01:10 • point

You're welcome John !

I can't wait to watch them :-)

  Are you sure? yes | no

John Croudy wrote 11/16/2019 at 06:30 • point

I've updated the links. I'm not sure that they are the exact same videos though because I had deleted them by accident so I couldn't verify them.

  Are you sure? yes | no

Yann Guidon / YGDES wrote 11/17/2019 at 01:16 • point

amazing ! Congrats again !

  Are you sure? yes | no

f4hdk wrote 02/18/2018 at 09:49 • point

Hello John.

I understand that you have finished the hardware : the 4 main CPU boards, plus additionnal I/O and video boards. Is that correct?

That's great. Contratulations!

Have you tested all the hardware?

I've seen also that you begin to write some PDF documentation on your website, and that you go on with the software part (assembler).

Do you plan to add new blog update, either here or on your blog? I would be happy to read that!

  Are you sure? yes | no

John Croudy wrote 02/18/2018 at 18:53 • point

Thanks. It seems to be working very well. It can run a self-test continuously for hours without going wrong. There were some very annoying mechanical oversights and several very 'interesting' problems getting it to be stable. The I/O still needs some work, but the video is working. I am planning to update the blog but I am behind and have so much to write it will take a while. I have been working on the assembler because the original version is a quick and dirty one which is buggy and under featured. I hope I have time to do all the things I have in mind for LEO-1.

  Are you sure? yes | no

Marcel van Kervinck wrote 02/18/2018 at 19:07 • point

A quick video of the tower of boards happily blinking along would be nice!

  Are you sure? yes | no

John Croudy wrote 09/24/2017 at 17:14 • point

Thanks :-)

  Are you sure? yes | no

Marcel van Kervinck wrote 09/23/2017 at 20:30 • point

Congrats for getting video to work for LEO-1!

  Are you sure? yes | no

John Croudy wrote 06/01/2017 at 18:48 • point

Thanks. I haven't had time yet to write about my flip-dot project. If you'd like I can send you the schematics...? It's actually 32x16 (two 16x16 panels).

  Are you sure? yes | no

Yann Guidon / YGDES wrote 06/01/2017 at 13:49 • point

What a beautiful work !

BTW you can have a look at #Dot flippers :-) I'm curious about your 24×32 array...

  Are you sure? yes | no

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