MIDI Standard Messages

MIDI serial data flows at the rate of 31.25 kilobits per second and is organised into 10-bit words. The first bit is called the START bit ( which is always 0 ), the next eight are the desired information, and the last is the STOP bit ( which is always 1 ). The start and stop bits delineate the desired data and provide the required synchronization but do not carry MIDI information themselves. A complete word is transmitted in 320 microseconds.

When we look as a digital word, 10010110, the bit at the far left is considered the Most Significant Bit. The remaining seven bits, 10010110, are considered the Least Significant Bits. Most MIDI messages consist of one, two or three bytes. Each byte may be classified as a status or data byte.

The eight-bit MIDI data is contained between the start and stop bits. There are two main types of bytes status and data. The lead bit of the status byte is always 1 and that of a data byte is always 0. This enables the microprocessor to distinguish between the two types of bytes and so make a corresponding decision.

So a MIDI message consists of a status byte followed by 0,1 or 2 data bytes. The MIDI message can be either a channel or system message. The channel message can be addressed to one of sixteen channels whereas a system message is addressed to all channels. The channel message can operate either on channel voices or on channel modes. The system messages provide real-time, common or exclusive control of the MIDI equipment.

MIDI MESSAGES

Table 1: Channel Voice Messages

Table 2: Channel Mode Messages

Table 3: System Messages

Table 4: MIDI Variables

For the Midi Message tables bbbb is a four bit binary nibble representing the MIDI channel from 0000 ( Channel 0 ) to 1111 ( Channel 15 ). The seven bit variables i.e. kkkkkkkk the MIDI key number range from 0000000 to 1111111 from 0 to 127.