Blizzard Lighting ProPar Seven 4, Руководство пользователя

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ProPAR 7.4 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 flexibility. 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 classification.
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 five 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 flows 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 defined standard.