Roland DG MPU-401 MIDI Processing Unit with 25 pin Interface cable & MIDI cable.

Perhaps most prized item in my possession is my Roland MPU-401 MIDI Processing Unit.  Equally as important is the interface card that came with it, the MIF-IPC-A.  The MPU-401 is essentially a computer in its own right, with a CPU, ROM, RAM and a bus interface.  The external unit contains all the intelligent circuitry and can be connected to an Apple II, a Commodore 64, an MSX, Sharp X1, a Fujitsu FM7 or an NEC PC-88 or PC-98 machine in addition to a PC compatible.  All you need is the appropriate adapter card or cartridge.  The external unit connects to the interface card/cartridge through a DB-25 male/male cable.  In my cable, pins 7, 8, 19, 20 and 21 are not connected and pins 13 & 25 are tied together (both GND).



Just as important, it came with all documentation and manuals.  It had the Roland MPU-401 Technical Interface Manual, the MPU-401 Booklet and the sheet for the MIF-IPC(-A) with the schematic on the back.  Finally, the equipment and manuals are in beautiful shape.  It didn't come with the box as I recall.  Later a friend of mine donated a second MPU-401 to me, but I don't have a second interface card for it.

What is the most important thing about this interface is what it represented.  The principal function of this interface was to connect to a Roland MT-32 or CM-32L (have both of them).  Unlike the Game Blaster, when a game supported the MT-32, the game almost always sounded best on it (not too hard when the competition was the Adlib Music Synthesizer Card and to a lesser extent the Game Blaster).  Roland LA Synthesis had a very long reign in the PC sound realm, from 1988 to 1992 when General MIDI devices began taking over.

The interface card provides two I/O ports to the interface at I/O 330 & 331.  By its design, it cannot use I/O 332-337 because pins A1 & A2 are unconnected  The traces next to the comparator allow it to be put virtually anywhere in the PC's 10-bit address space.  It can also use any interrupt request available on the ISA bus, but to use an IRQ other than the default 2/9, you also have to cut a trace.  Essentially the card is a traffic cop and a buffer for the 8 data bits and a few other signals.  It also supplies an Interrupt Request when the MPU-401 needs to assert an interrupt. The card uses a DB-25 female connector and bracket, four 74LS TTL logic chips and decoupling capacitors, one resistor and one electrolytic capacitor.  The card is as simple as you get and can easily be recreated.  You can find the schematic in my Tutorial : How to Get the Roland MT-32 working with DOS Games.  Without it, the complex interface unit is useless.



The card can be used in every PC compatible system, including PCs, XTs, ATs, Tandy 1000s and others.  The original MIF-IPC was a more complex card but has issues working in AT-class machines.  While the MPU-IPC and MPU-IPC-T can also work with everything, the interface is on the card, and if lost the breakout box is useless.  The last in the series, the MPU-401AT is not guaranteed to work in something less advanced than an AT system.  However, it was released in 1994 when the XT class machines were no longer a strong market segment, so it may not have been tested in them.  It is an 8-bit card, and probably will work without trouble in standard and near-standard (Tandy 1000) PCs.  However, it, like the MPU-401 SCC-1 and LAPC-I card go for very high prices when they are auctioned off on ebay.  MPU-IPC and MPU-IPC-Ts are often auctioned off incomplete.  In those cases, the card is important and the external MIDI IN and OUT ports can be recreated easily.

The MPU-401, MPU-IPC, MPU-IMC, MPU-IPC-T and LAPC-I all provide two MIDI OUTs.  Thus you can control a Roland MT-32 and a Roland SC-55 with one of these devices and not have to use a MIDI THRU, which can add latency and eventually lead to loss of data integrity depending on how many modules are in the Thru chain.  In practice, the first module in a MIDI THRU loop will be fine.

Thanks for looking!