Editing DMX512 (section)

== Physical layer ==

=== Electrical ===
<!-- Before revising this paragraph, please see section "Direct quotes from standards" on the talk page -->DMX512 data is transmitted over a differential pair using [[EIA-485]] voltage levels. DMX512 electrical specifications are identical to those of the EIA-485-A standard, except where stated otherwise in E1.11{{For example?|date=December 2018}}.

DMX512 is a [[bus network]] no more than {{convert|400|m}} long, with not more than 32 unit loads (individual devices connected) on a single bus. If more than 32 unit loads need to communicate, the network can be expanded across parallel buses using DMX splitters. Network wiring consists of a shielded [[twisted pair]], with a characteristic impedance of {{val|120|u=Ω}}, with a termination resistor at the end of the cable furthest from the controller to absorb signal reflections. DMX512 has two twisted pair data paths, although the specification currently only defines the use of one of the twisted pairs. The second pair is undefined but required by the electrical specification.

The E1.11 (DMX512 2004) electrical specification addresses the connection of DMX512 signal common to earth ground. Specifically, the standard recommends that transmitter ports (DMX512 controller OUT port) have a low impedance connection between signal common and ground; such ports are referred to as ''grounded''. It is further recommended that receivers have a high impedance connection between signal common and ground; such ports are referred to as ''isolated''.

The standard also allows for isolated transmitter ports and non-isolated receivers. It also recommends that systems ground the signal common at only one point, in order to avoid the formation of disruptive [[ground loop (electricity)|ground loops]].

Grounded receivers that have a hard connection between signal common and ground are permitted but their use is strongly discouraged. Several possible grounding configurations that are commonly used with EIA485 are specifically disallowed by E1.11.

=== Connectors ===
The original DMX512 1990 specified that where connectors are used, the data link shall use five-pin [[XLR connector|XLR]] style [[electrical connector]]s (XLR-5), with female connectors used on transmitting (OUT) ports and male connectors on receiving ports.<br />
The use of any other XLR-style connector is prohibited.

The three-pin XLR connector is commonly used for DMX512, on lighting and related control equipment, particularly at the budget/DJ end of the market. However, using three-pin XLR connectors for DMX512 is specifically prohibited by section 7.1.2 of the DMX512 standard. Use of the three-pin XLR in this context firstly presents a risk of damage to the lighting equipment should an audio cable carrying 48-volt phantom power be accidentally connected. Three-pin XLR designed for audio applications rather than DMX512 communications may also lead to signal degradation and unreliable operation of the DMX network.

DMX512-A (ANSI E1.11-2008) defined the use of eight-pin modular ([[8P8C]], or "RJ-45") connectors for fixed installations where regular plugging and unplugging of equipment is not required. Several manufacturers used other pinouts for RJ-45 connectors prior to this inclusion in the standard.

Other form-factors of connectors are permitted on equipment where the XLR and RJ-45 would not fit or are considered inappropriate, for example on equipment intended for permanent installation.

From ANSI E1.11 - 2008 section 7:
{{ quote box|width=90%|align=center
|quote=
7.1.2 Concession for use of an alternate connector (NCC DMX512-A)<br />
A concession to use an alternate connector is available only when it is physically impossible to mount a 5-pin XLR connector on the product. In such cases all the following additional requirements shall be met:<br />
1) The alternate connector shall not be any type of XLR connector.<br />
2) The alternate connector shall not be any type of IEC 60603-7 8-position modular connector except as allowed in clause 7.3.

7.2 Equipment intended for fixed installation with internal connections to the data link<br />
Fixed installation products with internal connections to the data link may use the 5-pin XLR connector, but shall not use any other XLR connector. When use is made of the 5-pin XLR connector, the requirements of 7.1 and 7.1.1 shall apply. When a non-XLR connector is used, this Standard makes no other restriction or stipulation on connector choice. The contact (pin) numbering on the alternate connector should match numbering for the standard 5-Pin XLR}}

==== XLR-5 pinout ====
# Signal Common
# Data 1- (Primary Data Link)
# Data 1+ (Primary Data Link)
# Data 2- (Optional Secondary Data Link)
# Data 2+ (Optional Secondary Data Link)

==== RJ-45 pinout ====
# Data 1+
# Data 1-
# Data 2+
# Not Assigned
# Not Assigned
# Data 2-
# Signal Common (0 V) for Data 1
# Signal Common (0 V) for Data 2

The [[8P8C]] modular connector pinout matches the conductor pairing scheme used by [[Category 5 cable|Category 5]] (Cat5) [[twisted pair]] patch cables. The avoidance of pins 4 and 5 helps to prevent equipment damage, if the cabling is accidentally plugged into a single-line [[public switched telephone network]] phone jack.

==== Common non-compliant connectors ====
In the early days of digital lighting control, equipment manufacturers employed various connectors and pinouts for their proprietary digital control signals. The most common of these is the three-pin [[XLR connector]]. When DMX512 was ratified, many of these manufacturers then issued firmware updates to enable the use of DMX512 control on their existing equipment by the use of a simple adapter to and from the standard 5-pin XLR style connector.

As the electrical specification currently only defines a purpose for a single wire pair, some equipment manufacturers continue to use it. Such equipment is not compliant with the DMX standard, but may be sufficiently compatible for operation using simple adapters.

There is a risk of equipment damage if 3-pin XLR audio and DMX signals are plugged into each other. 

===== XLR-3 pinout =====
Section 7 of ANSI E1.11 - 2008 prohibits the use of XLR-3 connectors with DMX512. However, in practice XLR-3 has become a de facto standard in the lighting industry with the following pinout commonly seen:
# Ground
# Data 1-
# Data 1+

Since DMX512 over XLR-3 is not officially standardised, there may be devices which use other pinouts.

===== Other RJ-45 pinouts =====
[[Color Kinetics]] has their own version of the RJ-45 connector for DMX,<ref>{{cite web |url=http://www.dl.colorkinetics.com/files/web/support/pro/wiring/RJ45_TO_RJ45.pdf |title=Archived copy |access-date=2016-06-28 |url-status=live |archive-url=https://web.archive.org/web/20160417220016/http://www.dl.colorkinetics.com/files/web/support/pro/wiring/RJ45_TO_RJ45.pdf |archive-date=2016-04-17 }}</ref> which predates the 2008 official inclusion in the DMX512 standard. The pinout specifically for Color Kinetics LED lighting products is:

# Data 1-
# Data 1+
# Shield
# Optional
# Optional
# Optional
# Optional
# Optional

=== Cabling ===
[[File:DMX Cable.jpg|thumb|upright|Cable built to the DMX512A specification]]

The standard cables used in DMX512 networks employ [[XLR connector#Five pin|XLR5 connectors]], with a male connector on one end and a female connector on the other end. The cable's male connector attaches to the transmitting, female jack (OUT), and its female connector attaches to the receiving, male jack (IN).

Cabling for DMX512 was removed from the ANSI E1.11 standard and a separate cabling standards project was started in 2003.<ref name="Control Protocols Working Group Meeting July 2003">{{cite web |url=http://tsp.plasa.org/tsp/working_groups/CP/docs/CPmin07-2003w.pdf |title=Archived copy |access-date=2011-08-11 |url-status=dead |archive-url=https://web.archive.org/web/20120330153032/http://tsp.plasa.org/tsp/working_groups/CP/docs/CPmin07-2003w.pdf |archive-date=2012-03-30 }}</ref> Two cabling standards have been developed, one for portable DMX512 cables (ANSI E1.27-1 – 2006) and one for permanent installations (draft standard BSR E1.27-2). This resolved issues arising from the differences in requirements for cables used in touring shows versus those used for permanent infrastructure.<ref name="PLASATSP" />

The electrical characteristics of DMX512 cable are specified in terms of impedance and capacitance, although there are often mechanical and other considerations that must be considered as well. Cable types that are appropriate for DMX512 usage will have a nominal characteristic impedance of {{val|120|u=Ω}}.  Also, cables designed for EIA485 typically meet the DMX512 electrical specifications. Conversely, microphone and [[line-level]] audio cables lack the requisite electrical characteristics and thus are not suitable for DMX512 cabling. The significantly lower impedance and higher capacitance of these cables distort the DMX512 digital waveforms, which in turn can cause irregular operation or intermittent errors that are difficult to identify and correct.<ref>{{Cite web|url=http://stage-directions.com/current-issue/55-light-on-the-subject/1949-troubleshooting-dmx-512.html%5C|title=Troubleshooting DMX 512|last=Cadena|first=Richard|date=2009-10-31|website=Stage Directions|language=en-gb|archive-url=https://web.archive.org/web/20190524190630/http://stage-directions.com/current-issue/55-light-on-the-subject/1949-troubleshooting-dmx-512.html|archive-date=2019-05-24|url-status=live|access-date=2019-05-24}}</ref>

[[Category 5 cable|Cat5 cable]], commonly used for networking and telecommunications, has been tested by ESTA for use with DMX512A. [[RJ45 connector]]s are used by some DMX-compatible hardware with ESTA standard<ref>[https://pinoutguide.com/Audio-Video-Hardware/DMX512_RJ45_pinout.shtml DMX (DMX512) RJ-45 pinout]</ref> or proprietary pinouts.