Blizzard Lighting Stealth ProPar (Rev A) - Manual (Page 14)

Page 14
ProPar Stealth Manual Rev. A Copyright (c) 2012 Blizzard Lighting, LLC
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 fl exibility. The
Entertainment Services and Technology Association (ESTA) has
since assumed control over the DMX512 standard. It has also been
approved and recognized for ANSI standard classifi 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
channels 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
transmission standard over two wires. As with microphone cables,
a grounded cable shield is used to prevent interference with other
signals.
There are fi 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 receiver, 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 fl ows only from
sources to receivers. Hence, most of us are most familiar with DMX-
512 as being employer over typical 3-pin “mic cables,” although this
does not conform to the defi ned standard.
DMX is connected using a daisy-chain confi guration where the source
connects to the input of the fi rst device, the output of the fi rst 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
fi xtures are used, the fi rst fi xture might be set to start at channel 1 so
it would respond to DMX channels 1 through 6, and the next fi xture
would be set to start at channel 7 so it would respond to channels 7
through 12.