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DMX 101



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DMX 101
Barry Abrams- Chauvet

What is DMX?

DMX 512 is a standard protocol by means of which lighting, controllers and control desks can communicate with lighting equipment. It was designed to allow equipment from different companies to be used together easily.

Where did DMX come from?

The first dimmers/fixture functions were actually controlled by levers on the dimmers/fixtures themselves.  During a show, it could take several men to move these levers and someone else to coordinate them. This kind of control was quite cumbersome. Later, control wires were run from each dimmer/fixture function to a control console. If you had 300 dimmers/functions, you had to have three hundred control wires! To improve this, manufacturers started using digital signals sent down one control cable. At first each manufacturer used their own protocols, meaning that different manufacturer's equipment could not be combined. Finally, DMX 512 was adopted as the standard lighting control protocol.

DMX has 512 individual channels, which can be set to a level between 0 and 255. If a dimmer/function was addressed to be on channel 1, and the level of channel 1 was brought up to 255 (or 100%), the dimmer/function would be sending out full power. Therefore, a color/gobo or other functions are assigned a number from 0 to 255.


Channel 1 Gobo
0 = Blackout
10-20 = Gobo 1
20-30 = Gobo 2
30-40 = Gobo 3

This means anywhere between level 10-20 gobo 1 would be visible.  DMX512: 512 represent the number of channels one DMX cable can carry. It requires only 3 pins. Older systems, known as 5-core DMX may be seen - (two pins will not be used and are reserved for 2nd data link). The data is sent serially to 2 pins (the third is the ground pin) known as "positive phase" or "hot" and "negative phase" or "cold". Pins 4 & 5 are reserved for 2nd data signal or talkback. At the console end, the channels are fed into a multiplexer (mux) which takes the individual channel's data and encodes it into a format suitable for sending down the DMX line with all the other channels' data. At the dimmer/fixture end, the data is fed into a demultiplexer (demux) and split up again into the individual channels to be fed to individual dimming/function circuits. In practice, the mux and demux will be incorporated into the console and dimmers respectively, though standalone mux and demux units are available to convert analogue systems into DMX required.

The DMX advantage

DMX is advantageous because the DMX cable is less bulky than a 48-conductor cable and is cheaper and less cumbersome. If the cable were required to run long distances, any repeater/amplifiers would only have to amplify 2 signals instead of 48. DMX also allows control of many different pieces of DMX equipment, such as smoke machine, scanners, dimmers etc. from a central location.

Who publishes the standard?

The DMX 512 standard (Actually USITT DMX 512 - 1990) is published by The U.S.I.T.T. it is now maintained by ESTA for more info on standards go to

Wire and Electrical details

DMX 512 is RS485 serial at 250K baud, as such any installation must meet the requirements of EIA-485. In particular use of suitable good quality cable is important (Mic cable is NOT suitable) suitable cables include:

  • Belden 9841

  • Belden 9842
  • Alpha 5274 This is not a complete list.  

Wiring practice

At the speed DMX works correct wiring practice is important. Always arrange wiring such that the data source is at one end of the cable. Never use an Y connector but rather a DMX splitter.

Line termination

All DMX lines must be correctly terminated if reliable operation is to be obtained. If not, signal loss can occur.  Some fixtures have a switchable line-terminating resistor built in. In these cases make sure that only the last item in the chain has its terminating switch set to the on position. If the last item (Farthest from data source) does not have a terminating switch then an external line-terminating network is needed. To make one you will need the following parts:

  • 1 Male 3 Pin XLR.

  • 1 110 ohm 0.5W resistor.

To make the line terminator solder the resistor across pins 2 and 3 of the XLR. You may like to back fill the XLR with epoxy resin to provide protection. Line termination will not correct a bad cable or interference from running a DMX cable next to an electrical cable. High power electrical cables will cause interference.  What is addressing?

Because the DMX protocol is so basic, each intelligent light's range of controlling DMX channels must be set manually. Each light's DMX address corresponds to the first of the light's channels.

For example:

If you have two intelligent lights that use five channels each. You set the DMX address of the first to 1 and the second to 6. Now, the first light is using channels 1,2,3,4, and 5; and the second is using 6,7,8,9, and 10.  You may also have to setup your intelligent light console for the type of lights you have and setup their DMX addresses on the console before you can control them.

Addressing Planning

You may want to do a little planning before you start addressing your lights. Put all your lights in a logical order; it will help you figure out which light is which later. Next, find out how many DMX channels each type of light you have uses. The light's manual should tell you this. Now that you know what channel to start addressing your lights at, you can figure each light's DMX address (except when your controller banks channels see Controllers). Take the first light's DMX address, add the number of channels it uses, and you have the second light's DMX address. Then, take the second light's DMX address, add the number of channels it uses, and you have the third light's DMX address. Do this until you have all the DMX address for your lights written down.


Some controllers (ShowXpress) give you settings automatically and some controllers use banks of channels.  Whether your fixture uses 4 DMX channels or 10 DMX channels it will still require you to set up your fixtures based on it banks.


CX-5 banks all fixtures in 14 channel intervals so your first fixture would always start on channel 1 and fixture 2 will always start on channel 15.

DMX-40 banks all fixtures in 16 channel intervals so your first fixture would always start on channel 1 and fixture 2 will always start on channel 17. DMX-40 has no joy stick there for you can use all the channels.

ShowXpress allows you to use all the channels

Setting dip switches

Read your fixture's manual to find out how to address your light. Many intelligent lights use binary dipswitches, while others lights may use a small display and buttons to set the DMX address. When using dipswitches there is always a minimum of 9 dipswitches. Each dipswitch has a value as listed below. If the first light starts at channel 1 (dip 1 on) and your second light starts at channel 40 (dip 4, 6 are on). Exception: if your controller works in banks of 14 you first fixture would start on channel 1 (dip 1 on) and 2nd fixture would start on channel 15 (dip 1,2,4,8 on) etc....

  • 1=1

  • 2=2
  • 3=4
  • 4=8
  • 5=16
  • 6=32
  • 7=64
  • 8=128
  • 9=256

Some fixtures have more then 9 dipswitches. 10 will always be a standalone function/ focus/ invert/self test etc....

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