DMX512(1990)Protocol.pdf

United States Institute for Theatre Technology, Inc. = U S I T T = DMX512/1990 DIGITAL DATA TRANSMISSION STANDARD FOR DIMMERS AND CONTROLLERS _ APRIL 1990 A Revision of the DMX512 Standard Published in August1986 A Project of the USITT Engineering Commission U S I T T 10 W. 19th St. - Suite 5A New York, NY 10011-4206 (212) 924-9088 (212) 924-9343 FAX DMX512/1990 Digital Data Transmission1.0 SCOPEThis Standard describes a method of digital data transmission betweencontrollersand dimmers. It covers electrical characteristics, data format, dataprotocol,connector type, and cable type.2.0 APPLICABILITYThis Standard is intended as a guide for:1. Equipment manufacturers and system specifiers who wish tointegrate systems of dimmers and controllers made by different manufacturers.2. Equipment manufacturers seeking to adopt a standard controller-dimmer digital transmission protocol.Although widespread adoption of this standard is sought by USITT,compliance withthe standard is strictly voluntary. Furthermore, it is not intendedas areplacement for existing protocols already manufactured, but ratheras an additionto existing protocols which will broaden the installed base ofcontrollers anddimmers that can communicate with each other.3.0 CROSS REFERENCESee EIA standards EIA-422A and EIA-485 available from: Electronic Industries Association Standards Sales Office 2001 Eye Street NW Washington, D.C. 2006 202-457-49004.0 ELECTRICAL SPECIFICATIONSThis standard shall follow EIA Standard EIA-485 (an enhanced versionof EIA-422A)with regard to all electrical characteristics including line driverand receiverselection, line loading, and multi-drop configurations.4.1 COMMON MODE VOLTAGESEquipment designers are advised to pay particular attention to theCommon Modevoltage provisions of EIA-485 in the choice of transmitter andreceiver componentsand general system implementation.4.2 ELECTRICAL ISOLATIONThis standard and EIA-485 make no general provisions for electricalisolation.However, suitable optical isolation, transformer isolation, or othermeans may beemployed to prevent the undesirable propagation of voltages whichexceed the CommonMode limits of EIA-485. The inclusion of such isolation does not,however, alterthe requirement that a transmitter or receiver conform to EIA-485. DMX512/1990 - 1 - April19905.0 DATA PROTOCOLData transmitted shall be in asynchronous serial format. Dimmerlevel data shall betransmitted sequentially, beginning with dimmer 1 and ending with thelastimplemented dimmer, up to a maximum of 512. Prior to the first leveltransmitted, aRESET signal shall be transmitted followed by a NULL START code.Valid dimmerlevels shall be 0 to 255 decimal (00 to FF hexadecimal) representingdimmer controlinput levels of OFF to FULL in a linear relationship. These numericvalues shallnot necessarily have any relationship to actual dimmer output, whichshall bedetermined within the dimmer itself.5.0.1 RESET SIGNALThe RESET signal (Timing Diagram, Designation #1) shall consist of aBREAK lasting88 uSeconds (two frame times) or any longer duration. A BREAK shallbe defined as ahigh-to-low transition followed by a low of at least 88 uSeconds.All dimmers andother receiving devices shall interpret any such BREAK as aterminator for anypending transmission/data packet and its end as the start of the MARKAFTER BREAKand START code sequence at the beginning of the next packet.5.0.1.1 MARK AFTER BREAKThe duration of the MARK seperating the RESET/BREAK and the STARTcode (TimingDiagram, Designation #2) shall be not less than 8 uSeconds and notgreater than 1Second. All DMX512/1990 transmitters shall produce a MARK AFTERBREAK of not lessthan 8 uSeconds. All receivers shall recognize an 8 uSecond MARKAFTER BREAK.Receivers capable of also recognizing the shorter 4 uSecond MARKAFTER BREAK (asspecified in the 1986 DMX512 Standard) may be identified and markedas having thiscapability as per paragraph 11.05.0.2 NULL START CODEThe NULL START code shall be defined as a properly framed NULLcharacter (all zeros)following a RESET. The NULL START identifies subsequent data assequential 8-bitdimmer level information.5.0.3 OTHER OPTIONAL START CODESIn order to provide for future expansion and flexibility, thisStandard makesprovision for 255 additional START codes (1 through 255 decimal, 01through FFhexadecimal). For this reason, a dimmer receiver must not accept as8-bit leveldata any data packet with a START code other than NULL STARTfollowing the RESET.5.0.4 MAXIMUM NUMBER OF DIMMERSEach data link shall support up to 512 dimmers. Multiple links shallbe used wherelarger numbers of dimmers are required. DMX512/1990 - 2 - April19905.0.5 MINIMUM NUMBER OF DIMMERSThere shall be no minimum number of dimmers on the data link. DMX512data packetswith levels for less than 512 dimmers may be transmitted, providedthat theconditions of this Standard, including Paragraphs 5.0 through 5.0.8,are observed.5.0.6 DEFINED LINE STATE BETWEEN FRAMESThe time between any two frames of a data packet (Timing Diagram,Designation #8)may vary between 0 uSeconds and 1 Second. The line must remain in amarking stateduring any such idle period greater than 0 uSeconds. A receiver mustbe capable ofaccepting a data packet having no idle time (0 uSeconds) between anyof its frames.5.0.7 DEFINED LINE STATE BETWEEN DATA PACKETSEvery data packet transmitted on the data link, regardless of STARTcode or length,must begin with a RESET, MARK AFTER BREAK, and START code sequence asdefined above.The time between the second stop bit of the last data byte/frame ofone data packetand the falling edge of the beginning of the RESET for the next datapacket (TimingDiagram, Designation #9) may vary between 0 uSeconds and 1 Second.The line mustremain in an idle (marking) state throughout any such periodgreater than0 uSeconds. Transmitters, therefore, must not produce multipleBREAKs between datapackets. Receivers, however, must be capable of recovering frommultiple BREAKsproduced by data link errors.5.0.8 MINIMUM BREAK SPACINGThe period between the falling edge at the start of any one BREAKshall be not lessthan 1196 uSeconds from the falling edge at the start of the nextBREAK.6.0 DATA FORMATThe data transmission format for each level transmitted shall be asfollows: BIT POSITION DESCRIPTION 1 Start Bit, Low or SPACE 2 through 9 Dimmer level Data bits, Least SignificantBit to Most Significant Bit Positive logic 10, 11 Stop Bits, High or MARK Parity Not transmitted7.0 DATA RATEThe data rate and associated timing shall be as follows:Data Rate 250 Kilobits per secondBit Time 4.0 uSecondsFrame Time 44.0 uSecondsMaximum UpdateTime for 512 dimmers 22.67 millisecondsMaximum UpdateRate for 512 dimmers 44.11 times per second DMX512/1990 - 3 - April19907.1 TIMING DIAGRAMSee Figure 1 for the DMX512/1990 timing diagram. Figure 18.0 LOSS OF DATA TOLERANCEThe receiving device must maintain, for a minimum of 1 Second, thelast valid levelreceived for each connected dimmer. Designers of transmitters arereminded that alow number of dimmer level (START CODE 00) updates may be interpretedby a receiveras a loss of data.8.1 RECEIVER DATA RATE TOLERANCEDMX512/1990 is intended to make possible the interconnection oflighting controlequipment by different manufacturers. It does not specify theminimum performancelevels of connected equipment, either by requiring a minimum numberof level updatesper second be produced by a transmitter, or by requiring that alllevel updates onthe data link be used by the receiver.The performance of any device incorporating a DMX512/1990 receivermust, however,not be degraded by the presence at its input of the continuoustransmission of datapackets containing any number of dimmer levels up to the maximumupdate ratesspecified in Section 5 and Paragraph 7.0 above. DMX512/1990 - 4 - April19909.0 CONNECTORSWhere connectors are used, the data link shall utilize 5-pin XLRstyle microphoneconnectors. Some manufacturers of this connector are: Switchcraft ITT Cannon Neutrik9.0.1 CONNECTOR SEXFemale connectors shall be utilized on controllers or othertransmitting devices andmale connectors shall be utilized on dimmers and other receivingdevices. In caseswhere an optional second data link is implemented using the sparepins of theconnector for bi-directional transmission, female connectors shallstill be utilizedon the controller.9.0.2 CONNECTOR PIN DESIGNATIONConnector Pin Designations shall be as follows:PIN 1 - Signal Common (Shield)PIN 2 - Dimmer Drive Complement (Data 1 -)PIN 3 - Dimmer Drive True (Data 1 +)PIN 4 - Optional Second Data Link Complement (Data 2 -)PIN 5 - Optional Second Data Link True (Data 2 +)10.0 CABLECable shall be shielded twisted pair approved for EIA-422/EIA-485use. Examples ofsuitable cables are: Belden 9841 Alpha 5271 (one pair, no spares provided) Belden 9842 Alpha 5272 (two pairs, one as a spare)11.0 MARKING AND IDENTIFICATIONEquipment conforming to this Standard may be marked and identifiedwithUSITT DMX512/1990 or DMX512/1990.Only receivers also capable of accepting a 4 uSecond MARK AFTER BREAKmay be markedand identified as USITT DMX512/1990 (4uSec) or DMX512/1990(4uSec).Compliance with this Standard is the responsibility of themanufacturer, and suchmarking and identification does not constitute certification orapproval by theUSITT. = END = DMX512/1990 - 5 - April1990This page contained a diagram refered to as fig 1 in text, herereproduced in ASCII | | | | | | |-1-| |4| |7| |4| |7| |4|7| |9| |2| |5| |6| |7| |5| |6| |7| |5|6| |7|-9|-1|_v v_v v_v_ _ _ _ _ _v_v_v v_v_ _ _ _ _ _v_v_v v_v_ _ _ _ _v_v_v v | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |_| |_|_|_|_|_|_|_|_|_| | |_|_|_|_|_|_|_|_|_| |_|_|_|_|_|_|_|_|_| | | |_| / /| BREAK START CODE (8) DIMMER 1 (8) DIMMER N|BREAK| OR| OR| RESET|RESET|