Page 13 – Blizzard Lighting SnowBlind (Rev A) User Manual

Page 13

Page 13

SnowBlind™ Manual - Rev. A

DMX is connected using a daisy-chain configuration where the source connects

to the input of the first device, the output of the first device connects to the

input of the next device, and so on. The standard allows 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 fixtures are used,

the first fixture might be set to start at channel 1 so it would respond to DMX

channels 1 through 6, and the next fixture 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 (indicating the

start of a new “packet”), a start code, and up to 512 bytes of data. Data pack-

ets are transmitted continuously. As soon as one packet is finished, another can

begin with no delay if desired (usually another follows within 1 ms). If nothing

is changing (i.e. no lamp levels 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 first 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 find 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 transmitted. 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 flexible, 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.