DMX512-A

This information is not complete (but may become in a few months) The purpose is to introduce the protocol and the details of a packet and maybe explain the required timing of the signal. --Beier 06:21, 28 January 2007 (PST)

Overview

A Universe contains 512 addresses and a single DMX line (cable) can only transmit one universe. I.e. a controller with two universes need two DMX lines (daisy chains including splitters). A uniververse is normally thought of as an address space (in the controller), the cables that transmits it and the equipment that receives it.

• The DMX signal is made up of a sequence which is sent over and over again (to increase robustness).
• The content is a "start byte" and 512 values, one value for every address.
• The address number is not sent over the lines, so the receiver must count the values from the start of the sequence to find the wanted value.
• A receiver must be set or programmed to an address it listens to. If a receiver listens to multiple addresses, the set one is the first.
• Multiple receiver can listen to the same address - the DMX system does not care.
• It is up to the controller/transmitter to decide how many addresses that should receive a value. Fever addresses means faster cycles.

The Packet

• Break
• Mark After Break (MAB)
• A frame contains the value for one address
• start bit
• Stop bits

Sources and additional reading:
Ujjal's DMX512 Pages
ePanorama
Wikipedia
USITT