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HAZARD
ALERT -- POWER on DMX512 DATA LINES |
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If you
use DMX512 equipment as part of your lighting
system, this is important to you. |
This page originally warned in 1997 that some equipment did not comply
with USITT's DMX512/1990 standard, as they placed between DC voltage on Pins
4 or 5 of their DMX512 connectors, in violation of the USITT DMX512 and DMX512/1990
Standards. In some cases, this DC voltage is even outside EIA-485's maximum voltage
range (EIA-485 is the electrical standard that DMX512 is built on).
Most products comply with the DMX512/1990
Standard -- this non-compliant voltage is not present on the data lines.
However some products are labeled DMX512 but do not comply. Some of these
non-compliant products have identification by a pin connection table adjacent to the
connector and have a modified circuit which is limited in current at the male
5 Pin XLR connector and is not linked through from male to female. This circuit is
claimed to be less likely to cause damage.
What the Standard says:
The standard clearly states that Pins 4 & 5 are for an optional second data link
(1)
and must conform to the electrical requirements of the EIA-485 standard
(2).
The standard also states the rules for marking the equipment indicating compliance
(3).
Placing a voltage on Pins 4 and/or 5 of the 5 Pin XLR connector compromises a DMX512
system and is a clear violation of the USITT DMX512, DMX512/1990, and ANSI E1.11 (DMX512-A) Standards.
Connecting DMX512, DMX512/1990, and DMX512-A compliant equipment that uses the secondary data link
(Pins 4 & 5) to
non-compliant gear may disable and/or damage compliant equipment.
In the Mean Time . . .
It should be pointed out that there are manufacturers that also do not use
Pins 4 & 5 in compliance with the standard, although it is unclear whether
such equipment is in production anymore. Only one or two may be using a voltage
outside of the EIA-485 specification.
So, if you use compliant DMX512 equipment that uses Pins 4 & 5 in accordance
with the standard, be aware that there is equipment out there claiming compliance
with DMX512, but does not comply and may in fact damage your equipment. If a
5 Pin XLR is used for something other than Fully Compliant DMX512, it
must not be labeled DMX512 (and should not even be labeled DMX).
Note that the use of a 5 Pin XLR connector on entertainment lighting equipment
has become synonymous with DMX512, even if not identified as DMX512. Therefore,
we recommend that 5 Pin XLR connectors only be used in accordance with the standard
and that manufacturers not fully compliant work to bring their products into full
compliance.
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1. Pin assignments as called out in the standards are
as follows:
PIN 1 - Signal Common (Shield)
PIN 2 - Data (Dimmer) Drive Complement (Data 1 -)
PIN 3 - Data (Dimmer) Drive True (Data 1 +)
PIN 4 - Optional Second Data Link Complement (Data 2 -)
PIN 5 - Optional Second Data Link True (Data 2 +)
2. The standards require adherence to
EIA-485 with regards to all electrical characteristics. EIA-485's maximum voltage range is
stated as -7 to +12 volts dc; +18 to + 25 volts dc is outside this specification.
3. The standards state rules
regarding the marking of equipment -- Only Equipment conforming to the Standards may be so marked.
Note - Compliance with these Standards is the responsibility of the manufacturer and
such marking and identification does not constitute certification or approval by USITT or
ANSI Accredited Standards Committee E1.
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