DMX512 Network topology

- Aug 27, 2017 -

A DMX512 network employs a multi-drop bus topology with nodes strung together in what is commonly called a daisy chain. A network consists of a single DMX512 controller – which is the master of the network — and one or more slave devices. For example, a lighting console is frequently employed as the controller for a network of slave devices such as dimmersfog machinesand intelligent lights.

Each slave device has a DMX512 "IN" connector and usually an "OUT" (or "THRU") connector as well. The controller, which has only an OUT connector, is connected via a DMX512 cable to the IN connector of the first slave. A second cable then links the OUT or THRU connector of the first slave to the IN connector of the next slave in the chain, and so on. For example, the block diagram below shows a simple network consisting of a controller and three slaves.

A simple DMX512 universe.

The specification requires a 'terminator' to be connected to the final OUT or THRU connector of the last slave on the daisy chain, which would otherwise be unconnected. A terminator is a stand-alone male connector with an integral 120 Ω resistor connected across the primary data signal pair; this resistor matches the cable's characteristic impedance. If a secondary data pair is used, a termination resistor is connected across it as well. Although simple systems (i.e., systems having few devices and short cables) will sometimes function normally without a terminator, the standard requires its use. Some DMX slave devices have built-in terminators that can be manually activated with a mechanical switch or by software, or by automatically sensing the absence of a connected cable.

A DMX512 network is called a "DMX universe". Each OUT connector on a DMX512 controller can control a single universe. Smaller controllers may have a single OUT connector, enabling them to control only one universe, whereas large control desks (operator consoles) may have the capacity to control multiple universes, with an OUT connector provided for each universe.

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