Owner manual

Page 15

DMXisconnectedusingadaisy-chaincongurationwherethesource

connectstotheinputoftherstdevice,theoutputoftherstdevice

connects to the input of the next device, and so on. The standard al-

lows for up to 32 devices on a single DMX link.

Eachreceivingdevicetypicallyhasameansforsettingthe“starting

channel number” that it will respond to. For example, if two 6-channel

xturesareused,therstxturemightbesettostartatchannel1so

itwouldrespondtoDMXchannels1through6,andthenextxture

would be set to start at channel 7 so it would respond to channels 7

through 12.

The greatest strength of the DMX communications protocol is that it is

very simple and robust. It involves transmitting a reset condition (in-

dicating the start of a new “packet”), a start code, and up to 512 bytes

of data. Data packets are transmitted continuously. As soon as one

packetisnished,anothercanbeginwithnodelayifdesired(usually

another follows within 1 ms). If nothing is changing (i.e. no lamp lev-

els change) the same data will be sent out over and over again. This is

a great feature of DMX -- if for some reason the data is not interpreted

thersttimearound,itwillbere-sentshortly.

Not all 512 channels need to be output per packet, and in fact, it is

veryuncommontondall512used.Thefewerchannelsareused,

the higher the “refresh” rate. It is possible to get DMX refreshes at

around 1000 times per second if only 24 channels are being trans-

mitted. If all 512 channels are being transmitted, the refresh rate is

around 44 times per second.

Insummary,sinceitsdesignandevolutioninthe1980’sDMXhas

becomethestandardforlightingcontrol.Itisexible,robust,and

scalable, and its ability to control everything from dimmer packs to

moving lights to foggers to lasers makes it an indispensable tool for

any lighting designer or lighting performer.