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What is DMX512? How does DMX512 controller work?

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What is DMX512 protocol

The DMX512 protocol is a data dimming protocol proposed by the United States Stage Lighting Association (USITT). It provides a protocol standard for communication between lighting controllers and lighting equipment. The proposal of this agreement provides a good standard for the use of digital signals to control lighting equipment.

The DMX512 protocol is suitable for master-slave communication, and its connection form generally adopts a multi-point bus structure. This structure has simple connections and high reliability. The data transmission mode specified by the DMX512 protocol is an asynchronous serial transmission mode. It uses the RS-485 interface standard to design the physical layer interface, which not only guarantees the data transmission rate, but also has better control capabilities for the dispersed network structure. For long-distance transmission, the accuracy of the data must be guaranteed, so RS-485 uses differential transceiver technology and balanced transmission in signal transmission. The differential transmission and reception of the signal improves the anti-interference ability of the signal, has a higher sensitivity in signal analysis, and ensures the long-distance transmission of the signal.

Analysis of DMX512 protocol format

The DMX512 control protocol stipulates that data is sent in the format of a data packet, and each data packet contains several data frames. The format of the data frame is shown in the figure below:


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(DMX512 data frame format)


The DMX512 protocol has certain requirements for the data transmission rate, the typical transmission rate is 250kbps. The corresponding duration of each bit is 4μs, and the duration of each data frame is 44μs, and the protocol also stipulates that each DMX512 data packet supports a maximum of 512 frames of data transmission at a time. The format of DMX512 data packet is shown in the figure below:

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(DMX512 data packet format)


The DMX512 protocol stipulates that data packets must be transmitted in accordance with the specified format and transmission baud rate. The format of a complete DMX512 data packet consists of an MTBP (Mark Time Between Packages) signal, a BREAK signal, a MAB (Mark After Break) signal and an SC (Start Code) signal, and other data frame. 

 

DMX512 controller module function

The DMX512 controller is divided into the following 6 functional modules, and the functional requirements for each functional module are as follows:

(1) LED light strip: The LED light strip is the main part of the controller that needs to be controlled. It is made up of full-color LED lights connected in parallel or in series. The display data is transmitted on the light string through the data line, so that The LED light string displays a specific effect.

(2) Manual control: The manual control part realizes manual control and adjustment of the controller, such as menu selection, switching of presentation effect files and adjustment of refresh rate between data packets, etc. Manual control is realized by buttons.

(3) LCD status display: The LCD part is mainly to provide a friendly operation interface through which the user can see which effect file is currently being demonstrated, the basic information of the effect file, and the refresh rate of the current demonstration file.

(4) SD card data: SD is used to save effect files, so if you want to replace the original demonstration effect, you only need to save the newly generated demonstration effect file to SD without modifying the controller and light string.

(5) PC-side online debugging: The PC-side online debugging is mainly to download to the controller immediately when a demonstration effect is generated, which facilitates the design and modification of the effect file. If the demonstration effect is ideal, the effect can also be directly saved to SD Card.

(6) Controller software: The control software part is the core part of the controller system. The main function of the controller is realized in this part, and other functional modules of the controller are combined and called to realize the controller's control of the LED light strip.