What is a MPU-401?
A MPU-401 refers to an interface or device that could connect music hardware with personal computers. The “MPU” stands for MIDI Processing Unit and so requires that the music hardware is equipped with this technology. The design of this device or interface is credited to the Roland Corporation, the same company who developed the MIDI or Musical Instrument Digital Interface standard. The first MPU-401 devices were released back in 1984 and became standard MIDI processing units for a time. These units are now obsolete though and have been replaced by newer technologies.
Back in the 1980s, MIDI interface devices or units were commonly included in the motherboards of IBM computers. Some MPU-401 units are also attached to the computer’s sound cards. Operation of this unit may be done using UART and Intelligent modes. When under the intelligent mode, the MPU-401 unit will be able to provide a time-stamp of potential MIDI events. This mode also allows for playback sequencing and automatic beeping depending on the rate of the timer. And since this mode has a variety of features and capabilities, its use may require some form of interruption handling for reasons that this unit literally interrupts the computer’s processes on a frequent basis. The MPU-401 also serves as the main controller using the built-in timer. In this way, all applications involved are directed on when the output of the succeeding MIDI message is to be displayed.
On the other hand, MPU-401’s in UART mode basically makes the unit a slave to the main personal computer. Its capabilities are limited and basically follow directions from the application involved. When a particular application writes a byte of information to the MPU-401, it will simply provide the output. But similar to the Intelligent Mode, this mode also has its own interrupt handler to handle simple interruptions to the computer processes. In its first release back in 1984, MPU-401’s were packaged in interface kits that are specific to the personal computer for connection with. Variations for the standard MPU-401 were released for the IBM PC, Apple II computers, Fujitsu FM7, and NEC PC-88/98 among various others.