ANSI E1.11-2008 pdf download American National Standard ANSI E1.11 – 2008 (R2018) Entertainment Technology—USITT DMX512-A Asynchronous Serial Digital Data Transmission Standard for Controlling Lighting Equipment and Accessories
4.4 DMX512 ports A DMX512 Port is the signal connection point between the internal electronics of a device and the physical transmission line (cable), referred to as the equipment interconnect points by EIA-485. It may be made either by the prescribed connector as defined in clause 7 or by a terminal strip. A DMX512 port carries four signals and a common reference, designated data 1-, data 1+, data 2-, data 2+, and data link common. (In some situations, data 2- and data 2+ are not connected /provided). Historically, these signals have been referred to as Pins which correlates to the physical pinout used on the XLR style connectors as defined in clause 7 of this Standard. There are other situations where different physical connections may be encountered, such as a terminal strip.
4.5 Data link common and grounding topologies Various portions of clause 5 and Annex A deal with shield-to-earth ground topologies. In all cases there is a low impedance connection between data link common pin or contact of the DMX512 port and signal common of the EIA-485-A driver or receiver circuitry.
4.6 Preferred method of earth grounding data link common DMX512 systems should make use of earth ground referenced transmitting devices and isolated receiving devices. This approach provides for a single point solid ground/chassis connection at the source, and allows for variations in building ground potentials between transmitting and receiving devices. This is to ensure that interoperability of equipment is achieved in situations that might otherwise exceed the Common Mode limitations of EIA-485-A. See EIA-485-A clause 4.3.1. Other approaches are covered in Annex A.
4.7 Primary data link Data 1- and Data 1+ of a DMX512 Port form the primary data link. Format of the data is covered in clause 8. Limited use of multiple data link drivers for half-duplex, bi-directional data transmission on the primary data link is permitted in accordance with Enhanced Functionality as described in Annex B. 4.8 Secondary data link Implementation of the secondary data link is optional.
4.8.1 Secondary data link – active use Data 2- and Data 2+ of a DMX512 Port provide a secondary EIA-485-A data link. Implementation of this data link is optional. Several different network topologies are associated with the implementation of the secondary data link. Use of the secondary data link is permitted only in accordance with Enhanced Functionality as described in Annex B.
4.8.2 Secondary data link – passive loop through ports In order to extend Enhanced Functionality across a network, devices containing two DMX512 ports, one for receive and one for transmit, that do not actively process or buffer data, shall provide a direct passive link for all signals between the two ports. Devices containing three or more DMX512 ports may provide a passive link between only two of the ports. These two ports shall be declared as required in Clause 10 and should be marked on the product. In order to enhance interoperability of DMX512 products, equipment designers are encouraged to provide passive loop through on the secondary data link pins or contacts whenever possible, even if not required per this clause.