DMX Primer
The USITT DMX512-A data transmission protocol (DMX, from now on) is based on
the EIA-485 standard and it has 512 channels (001 to 512). This system requires a
controller (DMX controller), one or more DMX compatible fixtures, and a DMX circuit
(also known as “DMX universe”) to link the fixtures to the controller.
Depending on their complexity and features, DMX compatible fixtures may require
from one to more than 30 DMX channels to operate. Some DMX fixtures have
multiple operation modes (also known as “personalities”), each with its own number
of channels and controllable parameters.
Starting Address
In the DMX system, the controller sends DMX data to each fixture based on the
fixture’s starting address. The starting address is the number of the DMX channel
(001 to 512) assigned to the fixture’s first control channel (Channel 1). When
assigning starting addresses to multiple fixtures, it is critical to ensure that no starting
address is already in use by another fixture to prevent channels from overlapping.
Otherwise, the affected fixtures may operate erratically.
For instance, a user has two DMX compatible fixtures. Fixture “A” has four channels
and fixture “B” has six channels. If the user configures the starting address of fixture
“A” to “001”, channels 001 through 004 on the DMX controller will control fixture “A”.
This means that the user should assign the starting address of fixture “B” to “005” or
higher. For a starting address of “005”, the DMX controller would use channels 005 to
010 to control fixture “B”.
It is possible to control multiple fixtures of the same type by assigning each one of
them the same starting address. In this case, all the fixtures would respond in unison
(synchronized) to the signals from the DMX controller.
Fixture Linking (Daisy Chain)
DMX compatible fixtures receive the control signals
from the DMX controller through the DMX cables.
Each fixture has a DMX In and a DMX Out
connector. The figure to the right illustrates how the
fixtures link to each other using multiple segments of
DMX cable in a sequential format called “daisy
chain”.
DMX
Controller
1st DMX
Fixture
The order in which the fixtures connect to the DMX
controller is irrelevant because all fixtures receive
the same DMX signals and they only respond to
them based on their individual starting addresses.
However, it is important to notice that the
connections between fixtures should always be as
short and direct as possible.
2nd DMX
Fixture
To other
fixtures
To ensure the integrity of the DMX signal, follow the
recommendations of the EIA-485 standard:
The maximum recommended cable length is 500 m (1,640 feet).
The maximum recommended number of fixtures on the same daisy chain is 32.
Connecting more than 32 fixtures on one daisy chain without the use of a DMX
optically-isolated splitter may result in deterioration of the digital DMX signal.
Cubix™ User Manual (Rev. 01a)
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