LED Followspot 75 User Manual (Rev. 07)
Page 15 of 17
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 products, and a DMX circuit
(also known as “DMX universe”) to link the products to the controller.
Depending on their complexity and features, DMX compatible products may require
from one to more than 30 DMX channels to operate. Some DMX products 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 product based on the
product’s starting address. The starting address is the number of the DMX channel
(001 to 512) assigned to the product’s first control channel (Channel 1). When
assigning starting addresses to multiple products, it is critical to ensure that no starting
address is already in use by another product to prevent channels from overlapping.
Otherwise, the affected products may operate erratically.
For instance, a user has two DMX compatible products. Product “A” has four channels
and product “B” has six channels. If the user configures the starting address of product
“A” to “001”, channels 001 through 004 on the DMX controller will control product “A”.
This means that the user should assign the starting address of product “B” to “005” or
higher. For a starting address of “005”, the DMX controller would use channels 005 to
010 to control product “B”.
It is possible to control multiple products of the same type by assigning each one of
them the same starting address. In this case, all the products would respond in unison
(synchronized) to the signals from the DMX controller.
Product
Linking (Daisy
Chain)
DMX compatible products receive the control signals
from the DMX controller through the DMX cables.
Each product has a DMX In and a DMX Out
connector. The figure to the right illustrates how the
products link to each other using multiple segments
of DMX cable in a sequential format called “daisy
chain”.
The order in which the products connect to the DMX
controller is irrelevant because all products 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 products should always be as
short and direct as possible.
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 products on the same daisy chain is 32.
Connecting more than 32 products on one daisy chain without the use of a DMX
optically-isolated splitter may result in deterioration of the digital DMX signal.
DMX
Controller
1
st
DMX
Product
2
nd
DMX
Product
To other
products
