Warning: There is not enough information in this repository to build your own card. The microcontroller, IC3, has not been dumped, and the logic in the gate array chip, IC2, is unknown.
Based on information available in the MPU-IMC service manual, here is an exact copy of the board layout. The MIDI Processing Unit is a way to connect digital musical instruments to a computer using the IBM MCA bus.
Further details on the card are available here.
There are two versions of this board in this repository. The first is a clone of the stock MPU-IMC. The second is a version that incorporates the circuitry of the external breakout box normally required for the MPU-IMC, including the optocoupler required by the MIDI specification.
If you're not sure which board you want to build, choose the modified card. It has several advantages:
- You will not need the external Roland breakout box.
- You can use the card bracket from a common IBM token-ring network card.
- The DE-9 connector uses the more common footprint.
There are some important caveats with this board set:
- IC2, the HG62E08, is a gate array chip customized by Roland. Think of it like a small CPLD but hard coded in ROM. I have no information on the internal schematic. Beware: not all HG62E08 parts will implement the same exact functions. Look for a Roland house part number, and make sure they match.
- IC3, the HD6801VD855P, is a custom mask-programmed microcontroller that runs the whole show. I have no ROM for this microcontroller. Before paying for expensive PC boards, make sure you have these chips first!
- The original (but NOT the modded card) has been built and works, see this thread on Vogons. The previous revision accidentally swapped pins 26 and 25 on IC3. This has been corrected for both the original and the modded card.
For fabrication, use a 2-layer process. You must specify a 30-degree edge bevel, other angles are probably OK but do not fab without a bevel at all because this may damage your MCA bus connectors! Technically you should get hard gold for the edge fingers, but that's usually expensive and immersion gold works just fine.
Following are reference materials for your convenience.
Please note that the DE-9 connector is NOT the standard connector commonly available--the distance between the mounting holes and the front plane of the connector is somewhat larger than usual. You may have to search surplus sources to find one that will fit, or modify the footprint.
Following are reference materials for your convenience.
The DE-9 connector uses the industry standard footprint and is readily available from Mouser. It's been relocated so that the card bracket from an IBM token ring network card (74F9321) will fit.
This work is licensed under a Creative Commons Attribution 4.0 International License. See https://creativecommons.org/licenses/by/4.0/.