Aglare Lighting DMX512 protocol and explanation
- date： 2021-12-28
- category： Industry knowledge
- click：
DMX512 protocol
1. Introduction to the protocol
DMX is the abbreviation of Digital MultipleX, which means multiple digital transmission. The DMX512 control protocol is an industrial standard for data transmission between lighting controllers and lighting equipment released by the United States Stage Lighting Association (USITT) in 1990. The full name is USITT DMX512 (1990), including electrical characteristics, data protocols, data formats, etc. .
2. Electrical Characteristics and Physical Layer
2.1.Electrical Characteristics
DMX512 adopts EIA-485 standard.
Transmitter: The logic "1" is represented by the voltage difference between the two lines + (2~6)V;
Logic "0" is represented by the voltage difference between the two lines as -(2~6)V;
Receiver: A is more than 200mv higher than B, which is considered to be a logical "1";
A is more than 200mv lower than B, which is considered to be a logical "0".
2.2.Topology
Figure 1 shows the EIA-485 circuit topology. An EIA-485 data link includes a differential line driver (D) and multiple differential receive terminals (R).
Figure 1 DMX512 topology based on 485
2.3.DMX512 port and data link
Because it uses 485 differential signal transmission, the DMX512 port generally adopts a 3-pin or 5-pin interface, and the corresponding wires are 1 pair or 2 pairs of twisted pairs, and the wires should be wrapped with foil or braided screen. The XLR pin assignments are shown in Table 1 below, in which the auxiliary data link may not be used.
effect | Definition of Needle in Standard | DMX512 function |
public place | 1 | shield ground |
primary data link | 2 (black) | Data 1- |
3 (white) | Data 1+ | |
Auxiliary data link | 4 (green) | Data 2- |
5 (red) | Data 2+ |
Table 1 DMX512 port signal assignment
Based on EIA-485, the transmission distance can theoretically reach 1200m, and it is recommended to control it within 800m. If you want to lengthen the transmission distance, you need to consider repeaters. The termination method of the DMX512 data link should eliminate signal loops and signal reflections, otherwise it may lead to misoperation of a properly designed system. The signal reflection can be eliminated by using the junction terminal resistor. The DMX512 standard requires that the terminal resistor should be placed between the data+ and data- signal pins, and the impedance range is 120Ω+5%~120Ω-10%.
The DMX512 protocol is a master-slave-based protocol that can adapt to one-to-many lighting control systems. Although this protocol can connect products of different manufacturers and implement control, due to only one-way transmission, the real information exchange between the console and the controlled device cannot be realized, and the controlled device can only passively receive the control information of the console , the state information of the controlled device itself cannot be fed back to the console. This protocol requires that the console must assign an address to the controlled device in advance, so that the controlled device can receive the control command without error. However, since there is no transmission address in the information frame structure, if there is an error in the transmission of a certain frame of signal due to interference or other reasons, then all the information after this frame will be mistransmitted, and the lamp cannot return the error information after the information is wrong. , which is the main reason for restricting the development of devices based on the DMX512 protocol.