12:13 am Projects

Here’s another cloned card for your retro PC: may I present the MPU-IMC clone! (The what?)

It’s a clone of an old card that Roland made for interfacing PS/2 computers (MCA bus) with MIDI equipment like musical keyboards.

Files may be found at GitHub.

Don’t get too excited though because it’s not complete. Well, the board layout and schematic are fine, but there are two chips on the board that are special.

  • The HD6801VD855P (Roland part number 15179222) is a mask-ROM microcontroller that runs the entire card. I’m not aware of anyone who’s dumped the ROM, but maybe now there is an incentive to do so. 😉
  • The HG62E08R10FS (Roland part number 15239133) is a gate array device. Think of a CPLD but these were “programmed” by customizing the top layer of metal during the IC fabrication process. Roland calls it the “Handshake controller” but nothing is known about the internal logic. If someone sacrifices a card and decaps this chip, a simple image of the top metal should be enough to deduce the functionality. There are rumors this chip is used on other Roland cards, but I am hesitate to say they are identical. I suspect Roland had various versions of this chip with different logic depending on the card and the computer’s bus. More work needs to be done.

Anyway, I hope this is useful to someone out there!

3 Responses
  1. Arbee :

    Date: January 5, 2019 @ 5:00 pm

    Incidentally, the gate array provides the two 8-bit bidirectional mail slots the host computer uses to talk to the 6801 and also generates the MIDI baud rate clock. In the normal version the ISA or MCA card is very tiny and has a thick cable going out to an external metal box containing the 6801 and gate array.

    Roland sold interfaces for at least ISA, Apple II, and Commodore 64 this way, but the non-PC versions are so rare I’ve only seen reference to them in the technical manual.

  2. Jens :

    Date: October 14, 2020 @ 9:03 pm

    Hi Eric,
    thanks for the great work.
    I thought I give it a try and produced a bunch of these boards.
    The two Roland chips I plan to scavenge from a working MPU-401 AT. (Part numbers match)
    What do you think, does it have a chance to work?
    If yes, I am willing to contribute to dumping the ROM / figuring out the logic IC.

  3. Jens :

    Date: October 24, 2020 @ 7:48 pm

    Hi Eric,

    I built the card and after some struggles it is almost working. I get some garbled music out of my MT-32. There is an error in the original schematics fro Roland that made it into the clone board. I could also gather some info about matching parts.
    Please contact me via email.
    Thanks and best regards,


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