MicroChannel MPU-401 controller
The Roland MPU-IMC was released in 1988 or 1989 for IBM PS/2 computers sporting the MicroChannel bus. It allowed the use of external MT-32 modules, or connecting any various General MIDI synthesizer. You could also synchronize a tape recorder for layering multiple 'takes' into a single track.
Out of the whole family of MPU-401 interfaces, this one has been the least dealt with and there's a lot of considerations to understand when working with a computer that has a MicroChannel bus. Some of those various 'considerations' addressed in later MPU-IMC cards.
--> MPU-IMC ADF File
The original Roland ADF diskette (came inside a jewel FDD case)
There were a total of three revisions:
Revision 1: Fixed IRQ, lacking extra PCB logic
Revision 2: Selectable IRQ, lacking extra PCB logic
Revision 3: Selectable IRQ, contains the extra PCB logic
The extra PCB logic as found on Revision 3.
I do not know what the extra PCB logic accomplishes in revision 3. From what I can tell, it doesn't affect anything obvious. The same issues that revision 2 has, revision 3 has.
The early MPU-IMC cards were hard-wired to IRQ 9; which apparently can conflict with the SCSI HDD controller on a PS/2 system. However, it is possible to run on IRQ 9 regardless. After I replaced the SCSI hard drive in a Model 95, it was able to use the MPU-IMC in IRQ 9 without hanging the system. This may be an ID conflict or something else-- haven't bothered to look into it in depth. I could not find any advantages on running the MPU-IMC in IRQ 9 over IRQ 5/7.
The MPU-IMC doesn't seem to be compatible with 100% of all MT-32 games. Strangely enough the games that have issues with the MPU-IMC are not usually (if at all) the 'intelligent' ones. Running on a faster machine (faster than a 486) seems to cause freezing in Windows 95 and the inability to add it as a MIDI controller. I am not sure if this is due to the use of low-speed schottkeys or a problem with windows, or a problem with how the device is designed for MicroChannel. Further testing in OS/2 pending.