Manual

Page 12

5. APPENDIX

A Quick Lesson On DMX

DMX (aka DMX-512) was created in 1986 by the United States Institute for

Theatre Technology (USITT) as a standardized method for connecting lighting

consoles to lighting dimmer modules. It was revised in 1990 and again in 2000

toallowmoreexibility.TheEntertainmentServicesandTechnologyAssocia-

tion(ESTA)hassinceassumedcontrolovertheDMX512standard.Ithasalso

beenapprovedandrecognizedforANSIstandardclassication.

DMX covers (and is an abbreviation for) Digital MultipleXed signals. It is the

most common communications standard used by lighting and related stage

equipment.

DMXprovidesupto512control“channels”perdatalink.Eachofthesechan-

nels was originally intended to control lamp dimmer levels. You can think of it

as512fadersonalightingconsole,connectedto512lightbulbs.Eachslider’s

position is sent over the data link as an 8-bit number having a value between

0 and 255. The value 0 corresponds to the light bulb being completely off while

255 corresponds to the light bulb being fully on.

DMX data is transmitted at 250,000 bits per second using the RS-485 trans-

mission standard over two wires. As with microphone cables, a grounded cable

shield is used to prevent interference with other signals.

TherearevepinsonaDMXconnector:awireforground(cableshield),two

wires for “Primary” communication which goes from a DMX source to a DMX re-

ceiver, and two wires for a “Secondary” communication which goes from a DMX

receiver back to a DMX source. Generally, the “Secondary” channel is not used

sodataowsonlyfromsourcestoreceivers.Hence,mostofusaremostfamil-

iar with DMX-512 as being employer over typical 3-pin “mic cables,” although

thisdoesnotconformtothedenedstandard.