Serial Communication Protocols

Serial communication protocols for data include the RS-232 protocol, which has been used for communication of modems. The MIDI protocol for music and sound applications is also a serial protocol.

Note: This is just a place-holder location for future development. Very little has been done with it to date.

RS-232 Serial Communication Protocol

The most common standard used for serial data transmission is called RS232C. It was set by the Electronics Industry Association and includes an assignment of the conductors in a 25-pin connector. It has also been used widely for data transfer over a modem.

Modem

For serial digital data transmission over telephone lines, the logic levels are converted to audio tones at one end (modulation) and then back into logic levels at the other end (demodulation). The device which accomplishes this is called a "modem" for "modulator-demodulator". The acoustic modem converts logic 1 to a 2225 Hz sine wave burst and a logic zero into a 2025 Hz tone. As a receiver it treats 1270 Hz as a logic 1 and 1070 Hz as a logic 0. This technique, called frequency-shift keying, allows the same phone line to be used simultaneously for sending and receiving in what is called full-duplex operation. The modem at the other end of the line must receive 2225 Hz as a logic 1 and send 1270 Hz as a logic 1. A basic rate of transmission is 300 baud, but data lines up to 56K baud are in use.

MIDI Communication Protocol

Musical Instrument Digital Interface (MIDI) is a serial data transfer protocol. It uses one start bit, eight data bits and two stop bits and operates at 31.25 kilobaud. It uses two lines for input devices and three lines for output devices. The controlling device and the instrument controlled are electrically isolated from one another by the use of an opto-isolator and the avoidance of direct common grounds. The controlling device sends a signal through a UART to a 5-pin DIN "MIDI out" connector. On the input side, the signal drives the LED of an optoisolator, and the output of the optoisolator is sent to the UART of the receiving device for conversion to parallel information.

In controlling a device in an integrated music system, the status byte describes the action to be taken while the data bytes provide specific values or other instructions for the type of action requested.

UART

The conversion of parallel data inside a computer to serial data for use in serial communication is accomplished by a Universal Asynchronous Receiver/Transmitter (UART). UART chips are used for RS-232 and MIDI communication.