New MOnSter6502 updates, with video!

12:29 am Uncategorized

It’s been a while since we’ve had an update to the MOnSter6502 project–we’ve been very busy getting the second revision ready. At the same time, I’ve been designing a simple yet powerful 6502-based computer that can operate at the slow clock speeds required by the MOnSter6502.

But before I go into detail about that, take a look at this video update. It’s one thing to see photos of the MOnSter6502, but the video really brings out just how awesome this thing is in person! (Shameless plug for Maker Faire Bay Area 2017 where you should come visit us.)

The MOnSter6502 runs up to about 60KHz clock, which is quite a bit slower than the original. The computer I’ve designed for it uses another microcontroller to simulate hardware peripherals, inspired by capabilities of various ’80s computers and gaming consoles. The idea is to offload CPU-intensive video and sound tasks to the microcontroller, freeing up the 6502 so that it can be used in real time despite the slow clock.

Right now, I’ve implemented several software-defined peripherals

  • VGA video output with 256 color graphics, tiles, and sprites
  • Multichannel stereo sound synthesizer
  • PS/2 keyboard interface
  • KIM-1 style front-panel debugging keypad and LED display
  • USB-CDC interface with a 6502-accessible UART for communications with a host PC

The computer can also run a full validation suite on the connected 6502, which has been quite useful troubleshooting the highly complex MOnSter6502 boards.

The computer is still a prototype, but you can see some shots of it in the video above.

You can find more updates and information at the project site.

11 Responses
  1. Ranayna :

    Date: May 19, 2017 @ 2:05 pm

    Great work!
    When I saw last years version published in a German Magazine (, I was already totally fascinated by this thing.
    And now you have made it even better…

    Now, I am sure I am not the first to ask…
    I want one, and I would like to build one myself. I think I have the soldering skill, and I definitely have the time 😉 But I doubt I have the skill to design it.
    I know from the FAQ that you will not create a DIY kit for this, but would you be willing to sell the board and provide a BOM?

  2. Dave :

    Date: May 24, 2017 @ 3:44 pm

    I love the idea of transistor-level processors and have been pondering one of my own. However, one of the pieces missing for what I want to do is four-terminal MOSFETs. I haven’t been able to find any so I’m quite interested in what part you found that brings out the substrate as a separate pin. Thanks.

  3. eric :

    Date: May 26, 2017 @ 10:46 pm

    Advanced Linear Devices has a whole line of MOSFET arrays with separate substrate pins.

  4. Dave :

    Date: May 27, 2017 @ 11:17 pm

    Thanks Eric. Those ALD MOSFETs look great.

  5. Olivier :

    Date: May 30, 2017 @ 3:32 pm

    Very nice accomplishment of major historical and pedagogical interest ! I realized a CPU only with EPROMs, but here I am really stunned :-).

  6. Steve Watts :

    Date: August 31, 2018 @ 2:44 pm

    You are MAD. This is just brilliant.
    Keep it up. I used to write games for the VIC-20 back in the early 80’s.
    I would love one of these.

  7. Vicent Colomar :

    Date: November 28, 2018 @ 6:06 pm

    Fantastic work Eric.

    Have you think in open source the schematic and pcb files, so everybody can try to build one? It would be great to show this to the computer students.

  8. Tim McNerney :

    Date: March 11, 2021 @ 6:23 pm

    This is awesome, Eric!
    I’ve been trying to do something similar with the Intel 4004, but you “beat me to the punch” with a more complex microprocessor.
    So… Kudos!

    I imagine that, after a few years of contemplating how to make your replica faster, you’ve determined it would be hard or expensive or both. Any wisdom you might share? Is it all about the gate capacitance of modern power FETs?

  9. eric :

    Date: March 11, 2021 @ 7:28 pm

    Thanks! Mostly it is a function of the saturation current rating of the series-pass FETs in combination with the gate capacitance of the power FETs used for the rest of the logic. No easy fix.

  10. Jusuf :

    Date: June 23, 2021 @ 9:44 pm

    Is it possible to get a schematic for the board? Or is it possible to buy just the board so i could make this myself?

  11. eric :

    Date: July 17, 2021 @ 10:41 pm

    Not at this point, it’s still an ongoing project.

Leave a Comment

Your comment

You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

Please note: Comment moderation is enabled and may delay your comment. There is no need to resubmit your comment.