MPU-401

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Roland MPU-401, opened.

MPU-401 ( MIDI Processing Unit ) was an important standard for MIDI interfaces for PCs, originally presented by Roland , which also took part in the definition of the MIDI standard.

The original MPU-401 was an external breakout box , which had connections for MIDI IN / MIDI OUT / MIDI THRU / TAPE IN / TAPE OUT / MIDI SYNC and together with a separately purchased expansion card / cassette specific to each computer system (so-called "MPU-401 Interface Kits") was operated. The following interface cards were offered for this combination:

Roland later moved most of the electronics from the breakout box to the interface card itself, reducing the size of the breakout box:

  • MPU-IPC: For the IBM-PC / IBM XT / IBM AT and compatible (8-bit ISA).
  • MPU-IPC-T: For the IBM-PC / IBM XT / IBM AT and compatible (8-bit ISA). The MIDI SYNC connection was removed and the I / O address and the IRQ line could be changed using jumpers for the first time .
  • MPU-IMC: For the IBM PS / 2 and its Micro Channel Architecture bus.
  • LAPC-I : For the IBM PC and compatible. Contains the Roland CM-32L sound source. The breakout box for this card (MCB-1) was sold separately.
  • LAPC-N : For the NEC PC-98 series. Contains the Roland CM-32L sound source. The breakout box for this card (MCB-1) was sold separately.
  • RAP-10: For the IBM AT and compatible (16-bit ISA). Contains a General MIDI compatible sound source. For UART mode only. The breakout box for this card (MCB-10) was sold separately.
  • SCP-55: For IBM Compatible Laptops ( PCMCIA ). Contains the Roland SC-55 sound source. The breakout box for this card (MCB-3) was sold separately.

Finally, the breakout box was completely dispensed with and all connections were moved to the back of the plug-in card:

Roland MPU-401 / AT
  • MPU-401 / AT: For IBM AT and compatibles. Contains a connector for wavetable daughterboards.
  • MPU-PC98: For the NEC PC-98 .
  • MPU-PC98II: For the NEC PC-98.
  • SCC-1 : For the IBM PC and compatible. Contains the Roland SC-55 sound source.

The MPU-401 can work in two modes: Normal and UART . In normal mode, things such as an 8-track sequencer , a metronome or the output of synchronization pulses are available to the host system ; Because of these features, normal mode is often referred to as “intelligent mode”, in contrast to UART mode, which reduces the MPU-401 to forwarding incoming and outgoing MIDI data bytes.

As the computers became more and more powerful, the possibilities of the “intelligent mode” have become superfluous, since it has become more efficient to provide them using appropriate software routines. Thus, the UART mode became predominant, which went so far that most compatible cards (e.g. Sound Blaster  16) no longer support "intelligent mode" at all.

While the Linux kernel to this day (2020, Linux V5.5.x) contains a driver for MPU-401, the Microsoft Windows operating system no longer offers any support for MPU-401 as of Windows Vista . However, Roland provides a driver that enables the use of MIDI modules on the RS232 port (Roland MIDI SerialOut Driver).