DMX512-A

DMX512-A is the colloquial name for a standard protocol called ANSI (American National Standard Institute) E1.11.

The development of DMX512-A was managed by ESTA (which, in 2011, became known as PLASA North America, or simply PLASA).

DMX512-A was previously called DMX2000. The DMX512-A standard replaces DMX512.

The key features of DMX512-A are:

Full backwards compatibility. This means that equipment designed for DMX512-A will work with DMX512 (1990).

DMX512-A defines higher levels of electrical protection for the data connection. This will benefit by reducing the potential for damage from static electricity or lightening strike.

A specific definition of the earthing practices that are allowed. Most of the compatibility problems between installed equipment have been caused by bad or incompatible earthing practices.

The use of pins 4 & 5 is specifically defined. These pins cannot be used for anything but RS485 data.

The connector usage is defined more specifically. Most important is the fact that the 3 pin XLR must not be used for DMX512. The main reason for this decision is to stop the confusion between DMX512 cables and audio cables.

Electrical isolation, also called optical or galvanic isolation, is now defined. DMX512-A does not mandate optical isolation. However, it does define the requirements for isolated equipment. It also suggests that the DMX512 receiver should be isolated, whilst the transmitter is grounded.

The System Information Packet or SIP is a new feature aimed at large installations. SIPs are transmitted at low frequency, by the lighting console, interleaved with normal lighting data. The SIP contains information about the console such as software revision, but also provides information such as the number of times the DMX signal has been processed. This could be passing through a merger or patching system. The SIP data can then be monitored at any point in the distribution chain.

Another new feature is the Text packet. This allows text information to be sent via the DMX512 signal. The key benefit is that ‘black box’ products that do not contain a screen are able to display text information such as operating status and software revision numbers.

The installation test packet is a special type of DMX512 data that contains the worst case type of data. Worst case means data that is most likely to make a data distribution problem visible. The benefit of this is that it becomes possible to test a DMX512 installation with a known type of data.

DMX512-A introduces a system of unique manufacturer identification codes. These allow processing equipment to be identified from anywhere within the installation.

This article provides a summary of some of the features of DMX512-A. The full standard can be purchased from PLASA.