ABSTRACT
When the Engineering Commission of the United States Institute of Theatre (USITT) set out to defi ne the DMX512 protocol, they chose to adopt an existing standard for the hardware used to transmit and receive data. As a result, the DMX512 standard defers to an existing standard from the computer electronics industry dealing with serial data transmission called TIA/EIA-485. It defi nes the electrical characteristics of generators and receivers used in balanced digital multipoint systems including the generator (in a DMX512 system this is the controller), the receiver (light, dimmer, fog machine, etc.), or transceiver (circuit with both a generator and a receiver), and the cable connecting them. It also defi nes important physical limitations and requirements such as the use of termination resistors, the total number of allowable loads (a load is defi ned as a passive generator, receiver, or transceiver), and the characteristic impedance of the interconnecting cable. Copies of TIA/EIA-485 Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multi-point Systems are available through IHS Global ( https://global.ihs.com ).
