Introducing the MOnSter 6502

MOnSter 6502 PCB

Our collaborator Eric Schlaepfer has been extremely hard at work this year, designing a truly monstrous follow up to our giant-scale dis-integrated 555 and 741 circuits. This is the MOnSter 6502: a transistor-scale replica of the famous MOS 6502 microprocessor, the processor found at the heart of influential early computer systems such as the Apple ][ and the Commodore PET.

It is huge, at 12 × 15 inches, with over 4000 surface mount components, and 167 indicator LEDs added throughout so that you can see the flow of data.

MOnSter 6502

This is a new project, still underway. We will be showing off the first prototype of the MOnSter 6502 at the Bay Area Maker Faire this coming weekend. We don’t promise that it will be completely working by then — this is a first stab at an extremely ambitious project — but we’re genuinely excited to show it off in this early stage.

Decode ROM

You can read more about the MOnSter 6502 on its main project page,, and at Eric’s blog,

(Before you ask, the MOnSter 6502 is not yet a kit or product that we’re selling. Right now, it’s an amazing thing that we’re trying to build. If you would like to stay in the loop as this project evolves, we’ve set up a special mailing list for updates.)

6 thoughts on “Introducing the MOnSter 6502

  1. I absolutely categorically must _DEMAND_ that you sell this as either a kit (ideally with a simple IO/RAM/ROM system to host it, but I suppose we can roll our own if needs be) some or at the very least as a bare board.

    In the immortal words of Fry; SHUT UP AND TAKE MY MONEY!

    Just think, Guinness book of records; world’s most complex single board soldering kit. Think of the accolades. Think of the groupies. Ok, on second thoughts, don’t think too hard about the groupies. We’re not exactly what dreams are made of.

    But think of the notoriety!

    Seriously. Do it. I dare you.

  2. What an amazing project!

    I seem to recall that there were expansion boards for the BBC micro (I still have mine in the loft incidentally) that could run at 2 MHz or 4MHz. I wonder whether that means that the other systems were comparatively independent of the main system clock…

    Really looking forward to seeing how this project develops.


    1. Yes, there was the solidisk 4M board, that could take a 4MHz CMOS version of the 6502 and plugged into the original 6502 CPU socket + a few extra flying leads for other control lines:

      But this needed its own Higher speed on-board RAM, as the Beeb’s normal DRAM was too slow and was also accessed on the CPU execute cycle by the 6845 CRTC which could only run at 2MHz.
      It took a tap off of an internal undivided 4MHz clock from the Beeb’s main board and probably switched to the 2MHz clock on the CPU socket / divided this dynamically, depending on what area of the memory map was being accessed – much like the Beeb slowing its clock down to 1MHz when accessing addresses on the ‘1MHz’ port.

      You could also connect a 6502 2nd processor to the ‘Tube’ connector, that orignally had a 3MHz 65C02 and later you could connect the Master Turbo 4MHz Co-processor board.
      The 2nd / Co-processor board essentially became the main processing computer, with 64K of usable RAM (48K to HiBasic) and the Beeb itself functioned as the I/O processor to deal with all the Peripherals

  3. I too MUST have one of these! Please make this a product. It will be fantastic for both teaching & display!

  4. Dare I suggest that I could remove the 6502 on my Apple II and plug this beuty in its place (with the appropriate jumper of course) and then be able to witness it working while i load up some vintage game?

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