DMX Primer EN
DMX Primer
Introduction
The Physical Medium
The Signals
DMX Universes
The Functions
DMX Primer Rev. 8
DMX (USITT DMX512-A) is a networking protocol that enables a universal DMX
controller to control the features of multiple DMX compatible products, whether
PAR cans, wash lights, moving heads, followspots, foggers, effect lights, or
proprietary product controllers, etc.
As any other networking protocol, the USITT DMX512-A describes the physical
medium, the signals, and the functions they control.
DMX-compatible products are connected to the DMX controller using a DMX
connection: a series of wired connections between the DMX controller and the
various DMX compatible products, also known as a daisy chain. In this type of
connection, the DATA OUT of one product or the DMX controller connects to the
DATA IN of the next product, and so on.
Each DMX product links to the previous and next DMX product or controller using a
DMX cable. This type of cable consists of a section of shielded, 2-conductor twisted
pair cable with one 3-pin or 5-pin XLR male connector on one end, and a 3-pin or 5-
pin XLR female connector on the other end. The XLR connectors pin-out is as
follows: pin 1 is the Common (shield), pin 2 is Signal Negative (S-), and pin 3 is
Signal Positive (S+).
Note: For DMX, pins 4 and 5 are not used.
The DMX signal stream is unidirectional from the DMX controller to the DMX
compatible products. These signals conform to the EIA-485 standard.
The stream of DMX signals consists of 512 individual, sequential channels that
form a frame. The DMX controller constantly sends frames of DMX signals to the
DMX connection, even if not all of the 512 channels are in use.
Because of this constant transmission method, there can be only one DMX
controller in a DMX connection. If not, the DMX signals sent by one controller would
interfere with the signals sent by the other controller(s).
A DMX universe is the set of DMX compatible products connected to the same
DMX daisy chain using the same set of 512 DMX channels. Each set of 512
channels is referred to as a DMX Universe.
In most cases, an installation will consist of only one DMX universe. However, you
might find it necessary to define two or more universes because of constrains
imposed by distance or the number of features.
Most DMX controllers support only one universe, although some DMX controllers
may support two or more universes. Each universe will have its own separated
DMX daisy chain. A DMX compatible product can only be part of a single DMX
universe.
Each DMX channel can have a value in the 000~255 range. Each DMX-compatible
product uses however many consecutive DMX channels as there are features the
user can control. The sequential numbers assigned to each DMX channel (1~512)
are also known as DMX addresses.
The function each DMX channel has, and the results of assigning a value to each
depend on the personality (or DMX channel layout) of each controlled product.
Some products only use a single DMX channel, while others may require 15 or
more DMX channels to control all their functions.
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