DMX512 -- Single-line 512 transmission technology innovation


New elf
Jul 20, 2020
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. Since it was proposed in 1990, the full name of the protocol is It is USITTDMX512 (1990). The proposal of this agreement provides a good standard for the use of digital signals to control lighting equipment.

The DMX512 protocol has certain requirements for the data transmission rate. The typical transmission rate is 250kbps, and the corresponding duration of each bit is 4us, and the duration of each data frame is 44us, and the protocol also stipulates each DMX512 data packet A maximum of 512 frames of data transmission is supported at a time. The format of the DMX512 data packet is shown in below.
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 MTBP signal, BREAK signal, MAB signal and SC signal, and the following data frame.

DMX512 includes single-line 512 products and dual-line 512 products; today I want to talk about single-line 512 products. The single-ine 512 needs to be connected to four pins, Signal A, Address , Positive pole, and Negative pole. The signal transmission distance is about 60 meters. Advantages: damage to any pixel does not affect signal transmission; Disadvantages: short transmission distance, easy to be interfered.

DMX512 adopts parallel data transmission mode, and a single data port needs to drive hundreds of signal receivers. Due to the long distance between the LED light strings is long in the LED lighting period, the ground potential of the LED decoding chip will be raised, which will cause serious interference to signal decoding. As shown in the figure below, when the LED light is on, the ground wire of the last decoding chip GS8512 will be raised. At this time, taking the ground level of the last question chip as a reference, the received DMX512 data is -1V-4V.

Ground level fluctuations will cause interference to the decoding of the parallel DMX512 signal single-line drive mode. Therefore, general engineering construction requires series grounding between power supplies to reduce ground level fluctuations. In order to better solve the impact of ground fluctuations on signal decoding, The Genesis-systech has proposed the C-frame decoding mode in GS8512/GS8513.

C-frame is a data frame feature parameter extraction and correction technology. C-frame will analyze the received DMX512 data frames in a certain period of time in real time to obtain different data fields such as the frame length (Tirame), field length (Tslot), code bit length (Tbit) and other values. Through the internal calculation unit of the chip, C-frame calculates the real-time pattern change characteristic values such as the code pattern time variability (data distorion), the code rate frequency domain fluctuation range (Direq), etc., through the pattern change characteristic value and the received data. For comparison, C-irame corrects the received display data for each frame, which can effectively restore signals interfered by ground voltage fluctuations.

The driver chip using C-frame data Correction technology effectively improves the decoding ability in a complex power supply environment, reduces the interference of ground level fluctuations on the chip signal decoding, and reduces the difficulty of engineering power supply installation.