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Table of Contents1. Introduction to DMX2. Industry Standards2.1 USITT2.2 ESTA2.3 ANSI2.4 EIZ/TIA2.5 References3. Theory of Operation3.1 The Cable TV Analogy3.2 DMX Communications3.3 Summary4. Protocol Specifications4.1 Connectors4.2 Cabling4.3 Data5. Sample Applications455566677101213131415165.1 Dimmer Control5.2 Intelligent Fixture Control5.3 Intelligent Fixture Control5.4 Distributed Control171819203

1. Introduction to DMXOften those of us plunged into the entertainment lighting industry, through work or circumstance, findourselves inundated with industry jargon and information overload. What is a moving head fixture, and howdo you control it? What is this DMX I keep hearing about? This handbook is designed to promote a basicunderstanding of the DMX 512 protocol. With this in mind, it covers the basics in theory of operation,proper equipment use, and some very basic sample applications.DMX 512 is a communication protocol, a set of rules, that are used to remotely control lighting-dimmersand intelligent-fixtures through a communication standard, a common way of communicating to theselighting devices regardless of the manufacturer. DMX is the acronym for Digital MultipleX, and 512 is theavailable number of control slots, or channels, for transmission. The 512 channels comprise a DMX‘universe’. In a simple dimming system, one channel controls the intensity of one dimmer. A singleintelligent fixture, however, may require several channels to control its various parameters (one channeleach for pan, tilt, color, gobo, etc.), and in many cases, functions or colors are controlled within a givenvalue range on a single channel as seen with the COLOR WHEEL on the sample chart below (especially inthe EXTENDED column). A basic dimming control console may support only a few of the 512 availablechannels, whereas many professional control consoles can support multiple universes, allowing forthousands of control channels.Sample channel list of a basicdimming control console with10 channels, where eachdimmer slide controls a specificfeature: Wheel PositionRedGreenBlueGobo WheelRotate ModeZoomFocusPartial Sample :Generic Moving Head DMX Channel Functions and ValuesMODE / CHANNELVALUEBASIC �127128–189190–193194-25554FUNCTIONPAN MOVEMENTPAN MovementPAN FINE MOVEMENT [16 BIT]Fine Control of PAN MovementTILT MOVEMENTTILT MovementTILT MOVEMENT [16 BIT]Fine Control of TILT MovementCOLOR WHEELOPEN / WHITEREDBLUEGREENYELLOWPURPLEAQUAORANGELIGHT PINKLIME GREENLIGHT YELLOWMAGENTACTBCTOUVCounterclockwise COLOR Rotation from FAST to SLOWNO RotationClockwise COLOR Rotation from SLOW to FAST

2. Industry StandardsBefore 1986, most manufacturers used their own proprietary control protocols, forcing system designersto mostly use fixtures and control consoles from the same manufacturer. Although there was no controlstandard to allow the use of a different manufacturer’s products, a number of companies developedadapters and patches for this purpose, which created control arrangements that were overly complex andsomewhat expensive.Given that a control standard comprises a set of widely agreed-upon guidelines for interoperability at bothcommunications and mechanical level, standardization of protocol and equipment provides many benefitsto manufacturers and end users, which include:-Increased product quality and safetyReduced development time and costSound engineering practicesGeneral cost savings via protection against product obsolescenceThe following organizations have developed standards that relate directly to the DMX 512 protocol:- USITT- ESTA- ANSI- EIA/TIA2.1 USITTThe United States Institute of Theatre Technology (USITT) supports, develops, and promotes a wide varietyof standards for the theatrical and entertainment industry. In 1986, USITT developed the DMX 512 protocolas a simple, flexible, and reliable standard for lighting control.In 1998, USITT transferred maintenance of the DMX 512 protocol to the Technical Standards Program ofESTA. The standard is constantly revised and updated as technology advances.2.2 ESTAThe Entertainment Services and Technology Association (ESTA) is a non-profit trade associationrepresenting the entertainment technology industry. ESTA promotes professionalism and growth in theindustry and provides a forum where interested parties can come together to exchange ideas andinformation, create standards and recommended practices, and address issues of training andcertification.5

2.3 ANSIThe American National Standards Institute (ANSI) is an organization composed of representatives fromindustry and government that collectively determine standards for the electronics industry as well as manyother fields, such as chemical and nuclear engineering, health and safety, and construction. ANSI alsorepresents the United States in setting international standards. New electronic equipment and methodsmust undergo extensive testing to obtain ANSI approval.In 2004, ANSI approved the DMX 512 standard, and has since approved several other related standardsincluding Remote Device Management (RDM) and Architecture for Control Networks (ACN). The actualstandards are listed below:-ANSI E1.11-2004 - Entertainment Technology USITT DMX512-A - Asynchronous Serial Digital DataTransmission Standard for Controlling Lighting Equipment and AccessoriesANSI E1.20 - Entertainment Technology RDM - Remote Device Management over USITT DMX512ANSI E1.17 - Entertainment Technology ACN – Architecture for Control Networks (MultipurposeNetwork Control Protocol Suite).2.4 EIA/TIAThe Electronics Industry Alliance (EIA) was a trade organization composed of representatives fromelectronics manufacturing firms across the United States. EIA began in 1924 as the Radio ManufacturersAssociation (RMA), and grew to include manufacturers of televisions, semiconductors, computers, andnetworking devices. The group set standards for its members, helped write ANSI standards, and lobbiedfor legislation favorable to growth of the computer and electronics industry. On February 11, 2011, the EIAceased operations.Although EIA ceased operating, several of its subgroups continue to operate autonomously, namely theTelecommunications Industry Association (TIA). The EIA/TIA-485 standard is the communication basis forDMX 512.2.5 ReferencesFor more information on any of these organizations or standards, visit their websites:- www.tiaonline.org6

3. Theory of OperationIn technobabble, DMX 512 is an asynchronous serial digital data protocol. This section will attempt toexplain how DMX operates in a simplified and easy-to-understand manner using a Cable TV Analogy andDMX Communications.3.1 The Cable TV AnalogyA central concept of DMX 512 is the ability to transmit data on multiple channels over a single cable. Tobetter understand this concept, imagine a simple cable TV system with four major components: a CableTV Company, a Cable, a Decoder, and TV.The DMX Control Console will broadcast up to 512 channels over one DMX Cable. Some of these channelsmay not be used, but will still be transmitted, as required by the protocol. The Decoder in this example isbuilt into the Dimmer. It must be set to a desired channel (channel 001, in this example) to control theconnected Light Fixture. This is usually accomplished using a DIP switch (manual electric switch), orLED/LCD display. This desired ‘channel’ is commonly known as the DMX address.7

Now imagine a simple DMX system where the Cable TV Company is the DMX Control Console, the Cableis the DMX Cable, the Decoder is the DMX Decoder built into a Dimmer, and the TV is the Light Fixture.The DMX Control Console will broadcast up to 512 channels over one DMX Cable. Some of these channelsmay not be used, but will still be transmitted, as required by the protocol. The Decoder in this example isbuilt into the Dimmer. It must be set to a desired channel, as with the previous example, starting withchannel 001 to control the connected Light Fixture.8

Many DMX devices, such as dimmers and intelligent fixtures, are capable of receiving several controlchannels at once. If a Dimmer has four channels capable of controlling four Light Fixtures, it must knowwhich four control channels to receive. This is accomplished by setting a ‘base address’, or the DMXaddress for the first Light Fixture, channel 005 in this example. The remaining Light Fixtures will becontrolled by the next three sequential control channels. The DMX Decoder knows it needs only these fourcontrol channels, and will ignore the rest.9

3.2 DMX CommunicationsIn the world of digital communications, information is sent using precise electrical voltage pulses. A positivevoltage pulse represents a 1, on, and a zero-voltage pulse (or no voltage) represents a 0, off. Systemsusing 1’s and 0’s to encode information are called binary systems (a bicycle has two wheels, a binary starsystem has two suns).Each pulse in a digital signal is called a binary digit, or bit. A bit can only have one of two values, 1 or 0. Agrouping of eight bits, called a byte, is used to carry one piece of information. This ‘information’ is simplya value ranging from 0 to 255.The most common method of transmitting digital signals is to send data one bit at a time in one directionover one wire. Since each bit is transmitted in series, this method is known as Serial Communication. Inits simplest form, Serial Communication requires one data wire for transmission and one commonreference (or ground) wire.There are two types of serial communication: asynchronous and synchronous. With asynchronous datatransmission, data is sent one byte at a time, which means that asynchronous devices do not requireperfect synchronization (a “not”, syn “together”, and khronos “time”). That said, their timing signals (pulses)still need to be somewhat close [at least within a plus or minus 5% range of the data sampling clock circuit,which makes this method relatively simple and inexpensive]. [A data sampling clock circuit is datasent/received relative to its clock position, wherein a stream of data has information in the beginning,center, and end to signal the position of the data within a given or known period (data rate)]. Think of a fivesecond long data signal, which can be sent at a relatively arbitrary time (plus or minus 5% of the clockcircuit used), and know that once the beginning of the signal is received, it signals that it will last exactly5-seconds, with another signal to mark its end. With synchronous data transmission, data is sent as agroup of characters in a single stream of bits known as a bitstream. Synchronous serial digital data protocolrequires precise and expensive synchronized devices at both ends.There are many standards for Serial Communications, each having its own advantages and disadvantages.Communications standards generally fall into two broad categories:-Single-ended (unbalanced)Differential (balanced)The single-ended specifications allow for data transmission from one transmitter to one receiver atrelatively slow data rates and short distances. When communicating at high data rates, or over longdistances in real-world environments, single-ended transmission methods are often inadequate.Differential data transmission offers superior performance in most applications by helping to nullify theeffects of interference on the signal. This is achieved by using two wires to transmit the signal (withopposing polarity) instead of just one.The DMX 512 protocol is based on the EIA/TIA-485 standard (commonly known as RecommendedStandard 485 or RS-485), which uses asynchronous differential data transmission. This standard supports32 devices on one network at a distance of up to 4000 feet. One device functions as the master (the DMXcontroller) on a network, while the rest function as slaves (dimmers, intelligent fixtures, etc.). Only themaster transmits over the network, and all slaves receive the same data.10

While 4000 feet may be specified by the standard, most manufacturers recommend DMX runs of no morethan 1000 feet (300 feet between devices) before using a repeater to regenerate the signal. Each deviceshould have input and output connectors, but these are usually wired so that there’s no re-transmissionor amplification.Devices are connected in a daisy-chain fashion, from the controller to device #1, then device #1 to device#2, and so on. The final device in the daisy-chain must be terminated. The terminator absorbs signal powerwhich would otherwise be reflected into the cable and degrade the data. A terminator simply places a 110120 Ohm, 0.5-Watt resistor across the two transmission wires.NOTE: DMX cannot be split reliably by making Y-cables or T-connectors. DMX splitter/repeaterstypically use optical isolation to protect each segment from electrical faults on other branches.These can be used to increase the number of devices on one network beyond the limit of 32. Eachbranch of a splitter/repeater can support up to 32 devices.11

3.3 SummarySo how does all this information relate to controlling a light fixture? Think of it in terms of the simple DMXController Console. The console may have up to 512 control faders on it (8 in this example). Each fadercontrols the intensity of one light (using one DMX Channel). The position of the fader represents an 8-bitvalue (DMX Value) between 0 and 255, where 0 is off and 255 is full on.Up to 32 devices may be connected in a daisy-chain, with a terminator on the last device. Using a DMXsplitter/repeater (opto-isolator) can extend both cable distance, as the signal is regenerated andretransmitted, and the number of devices, up to 32 per branch.12

4. Protocol SpecificationsUnderstanding how DMX 512 operates is important, but it’s only part of the picture. The physicalequipment, connectors and cabling, play a critical role in the proper functionality of the protocol. The DMXstandard specifies exactly what types of connectors and cable may be used.It is also important to understand the logic behind the data that is transmitted. Data is sent in a specificmanner so that the receiver can correctly translate it into action.The topics this section will cover are: Connectors, Cabling, and Data.4.1 ConnectorsThe DMX standard specifies 5-pin XLR connectors. The name comes from the original manufacturer(Cannon X connector, with a Latch and Rubber guard).Only three of these pins have standardized use however, leading many companies to make use ofinexpensive and readily available 3-pin XLR connectors.The remaining two pins are in place for potential future usage, such as allowing connected devices tocommunicate information back to the controller (lamp hours, operating temperatures, etc.).Pin12345DMX 512 Connector PinoutWireShield DrainInner Conductor (Black)Inner Conductor (White)Inner Conductor (Green)Inner Conductor (Red)SignalGround / 0VData Data Data – (Spare)Data (Spare)NOTE: Many manufacturers use pins 4 and 5 for non-standard applications, often using voltagesthat are potentially dangerous to DMX compliant devices. Such applications are meant only for usewith approved devices (usually from the same manufacturer). Use with standard DMX devices cancause serious damage to equipment.13

4.2 CablingStandard DMX 512 requires twisted-pair, shielded, low-capacitance data cable designed for RS-485.Inner JacketOuter JacketPair 1DrainPair 2ShieldThe twisted-pair configuration ensures that any interference affects both signals equally. This practice iscommon to good data cable, helping the signal driver eliminate any interference. The cable shield alsoprotects against interference. A shield ‘drain’ wire makes connector installation easier.There are many cabling characteristics to consider when designing a system. The following list contains afew such characteristics for consideration:-Impedance (110-120 Ohm recommended)Capacitance ( 25 pF cond.-to-cond., 40 pF cond.-to-shield recommended)AttenuationNumber of conductors/pairs (minimum 1 pair)Number of twists per footConductor material/diameterWire gauge (AWG)Maximum current and temperatureInner and outer jacket materialMinimum bend radiusMaximum pull tensionNOTE: Many people often substitute a cheaper balanced audio cable (regular microphone cable) withtragic results. An audio cable cannot support the signal rate required by the high speed DMX protocol.While the signal may pass over short distances, it is highly susceptible to interference anddegradation, causing unpredictable results (such as blinking lights, confused intelligent fixtures, etc.).14

4.3 DataDMX 512 data is transmitted at 250 kilohertz (kHz), meaning that a maximum of 250,000 1’s and 0’s canbe sent each second. Each bit is measured in 4 microsecond (μs) intervals. In order for the receivingdevice to correctly interpret the data, it must be sent in a particular sequence. A single transmission(DMX Packet) includes synchronizing elements and channel data for up to 512 channels.Channel 1BREAKMABSCMTBFCDMTBFChannel 2Channel 512CDCD MTBFMTBPThe following table describes each element of the DMX Packet (illustrated above), including its line state, size,and duration. An idle DMX line will have a continuous HI (1) line state.DMX PacketDescriptionThe Break resets the line, signalingBreaka new DMX PacketInner Conductor (Black)Mark After Break (MAB)The SC is identical in size toStart Code (SC)channel data, but always 0 in value.Mark Time Between Frames The MTBF is used to space outindividual data bytes.(MTBF)The CD carries the 8-bit DMX ValueChannel Data (CD)for each channel, plus one start andtwo stop bits.Mark Time Between Packets The MTBP is used to space outentire DMX Packets.(MTBP)ElementStateLO (0)SizeDuration22 – 250kbits 88µs -1 sec.HI (1)Mixed2 – 250kbits11 bitsHI (1)0 – 250kbits Up to 1 sec.MixedHI (1)11 bits8µ - 1sec.44µs44µ0 – 250kbits Up to 1 sec.NOTE: At a minimum, a fully loaded DMX Packet (data for all 512 channels) will be around 5700bits. This means about 44 DMX Packets can be sent each second.WARNING: DMX 512 has no error prevention, and is prohibited from use in life-safety applicationssuch as pyrotechnics, or set / rigging motion control.15

5. Sample ApplicationsThe figures on the following pages illustrate several different applications using various DMX products.Samples include:- Dimmer Control- Intelligent Fixture Control- Dimmer & Intelligent Fixture Control- Distributed ControlAs mentioned earlier, dimmers normally use one DMX Channel per light. They translate DMX Values in alinear fashion, with 0 being off and 255 full on.Intelligent fixtures use one DMX Channel per parameter (such as pan, tilt, color, gobo, etc.). How does thecontroller know which channel controls each parameter? Each intelligent fixture has a DMX ChannelMapping that matches control channels and parameters.- Channel 1: Pan- Channel 2: Tilt- Channel 3: Color- Channel 4: Gobo- Channel 5: DimmerPan and tilt functions are linear, but color and gobo functions present a challenge. Imagine a wheel withsix colors plus open (no color). How does the controller tell the fixture which color to use? The fixtureassigns a DMX Value Mapping to each color.- 0-35: Open- 36-70: Red- 71-105: Cyan- 106-140: Green- 141-175: Yellow- 176-210: Blue- 211-255: MagentaThe DMX Channel and Value Mappings are typically saved into a computer file for each DMX controller.This file is called a Fixture Profile. In order to use a particular fixture with a controller, a current profile mustbe loaded. Most controllers come pre-loaded with thousands of fixture profiles from many differentmanufacturers.16

5.1 Dimmer Control17

5.2 Intelligent Fixture Control18

5.3 Dimmer and Intelligent Fixture Control19

5.4 Distributed Control20

3.1 The Cable TV Analogy A central concept of DMX 512 is the ability to transmit data on multiple channels over a single cable. To better understand this concept, imagine a simple cable TV system with four major components: a Cable TV Company, a Cable, a Decoder, and TV. The DMX Control Console will broadcas