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  • DMX Speed

    DMX-512 has a number of timing variables. The information presented here will probably be useful for only a small proportion of users, but can assist in getting troublesome DMX equipment to work. If you need further information, the book "Recommended Practice for DMX512: A guide for users and installers" is highly recommended and available from The Esta Foundation.

    DMX Timing

     

    There are several areas where DMX timing can vary in a DMX packet. Each packet follows the format shown above.

    First, a break occurs telling the receiver that this is the start of a new packet. Then the line is driven high for the Mark after Break (MAB) time. Then follows the start code, followed by the "post start" time. Then there follows the channel data, during which the line can be high (idle) for a variable amount of time between channels, known as the interbyte time. Finally after the last channel the line goes high (idle) for the interpacket delay time until the break of the next packet.

    The following are the minimum values allowable by the ESTA DMX-512A standard :

    Timing Parameter MinimumMaximum
    Break92μsNote 1
    Mark-After-Break12μsNote 1
    Post-Start8μs (Two stop bits) Note 1
    Interbyte8μs (Two stop bits) Note 1
    Interpacket8μs (Two stop bits) 

    Note 1

    Note 1 : These timings can be any value to add up to make a packet length of up to one second.

    As you can see a very wide variety of timings is permissible. For reference, here are the timings for some different ETC products.

     

    Ion, Element, Congo, Congo jr and Congo Kid Consoles

     Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum36142128241212
    Fast36142128271816
    Medium36142128343030
    Slow36142128424644

     

    Smartfade, Software Version 3.0.0

    Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum0176162200
    Fast12176442742000
    Medium1622010034164000
    Slow3626410050368000

     

    Express, Software Version 3.1

    Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum32942626121160
    Fast321382826121160
    Medium321843226122120
    Slow322705031126960

     

    4 Port Net3 Gateway, Software Version 5.1.0, ACN Mode

    PORTS 1&2Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum81761222.88180 - 432
    Fast1219260 25.3122320
    Medium122406025.3124260
    Slow12 2886025128320
    PORTS 3&4Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum81941223.98150-400
    Fast121884825.2 122260
    Medium12 2406425.3 124140
    Slow122726445 488560

     

    4 Port Net3 Gateway, Software Version 4.0.5.9.0.36, Net2 Mode

    Observations

    • Variable DMX output speed is not implemented
     Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Any8126-13256248784-1260

       

    2 Port Net3 Gateway, Software Version 4.0.5.9.0.36, Net2 Mode

    Observations

    • Variable DMX output speed is not implemented
     Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Any8176122381260

     

    2 Port Net3 Gateway, Software Version 1.0.0.9.0.83, ACN Mode

     Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum817612228176
    Fast8176122482160
    Medium122406029124200
    Slow132886033128240

     

    2 Port ETCNet2 Node, Software Version 4.1.3.9.0.6

     Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum888-93482288
    Fast1215648251290
    Medium16184742716162
    Slow242261003124254

     

    Four Port ETCNet2 Node, Software Version 4.1

     Post Start (μs)Break (μs)MAB (μs)Packet (ms)Interbyte (μs)Interpacket Idle (μs)
    Maximum89482381140
    Fast8142132683040
    Medium8188182785160
    Slow828233-353288800