Page 15 – Blizzard Lighting FX SnowBlind (Rev B) User Manual

Page 15

Page 15

SnowBlind™ FX Manual - Rev. B

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 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
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 (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 finished, 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 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 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 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.