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What is DMX512? Advantages and disadvantages of DMX512 protocol
1. Use one-way communication.
2. DMX512 communication needs to transmit an 88us low-level data as the starting frame header of a packet of data. The receiver has a gap detection circuit and needs to find the data starting frame header. There is no communication check.
3. The fixed baud rate of DMX512 communication is 250kbps. Due to the open communication protocol, high efficiency and reliability, it is widely used in the traditional stage industry. The compatible DMX512 communication interface has become the default choice in the LED outdoor lighting control system. Its advantage is that the transmission distance is long and it belongs to the bus protocol. Its bad points will not affect the following points. Many large-scale night scene lighting projects and bar lighting controls use DMX512 signal lamps.
2. Electrical Characteristics
DMX512 adopts the EIA-485 standard. Sending end: Logic "1" is represented by the voltage difference between the two lines + (2 ~ 6) v; Logic "0" is represented by the pressure difference between the two lines - (2 ~ 6) v; Receiving end: a is 200mv higher than b The above is considered as logic "1"; if a is more than 200mv lower than b, it is considered as logic "0".
Detailed explanation of DMX512 protocol
The dmx 512 transmission rate is fixed at 250kbps. The time for each data bit is 4us. Each byte is eleven bits, which is 44us. 1 second = 1000 milliseconds 1 millisecond = 1000 microseconds. Therefore, the data transmission time of 512 bytes is 44 *512=22.528ms The frame header of the data is usually 88us. The frame header of the data is followed by an idle frame. The length of the idle frame is 8us-1ms. There is a byte before the 512-byte data packet, indicating the device code or Custom purpose, usually 0, the data of this byte can be used by automatic code writing command.
Three characteristics
Compared with other protocols, the DMX512 protocol has the following characteristics:
(1) The signal is transmitted based on differential voltage and has strong anti-interference ability;
(2) Using RS-485 bus transceiver, signals can be transmitted over long distances;
(3) Data refresh is fast. Regardless of whether the dimmer output needs to be changed, the host must send a control signal. The time between data frames is less than 1s. If the dimmer does not receive a new data frame within 1s, , you will know that the data has been lost;
(4) Simple to implement and does not require special hardware equipment support
Four disadvantages of the DMX512 protocol include:
The main disadvantages of the DMX512 include that it does not include automatic error checking and correction, making it unsuitable for hazardous applications such as pyrotechnics or the movement of stage equipment. Electromagnetic interference, electrostatic discharge, incorrect cable termination, cable length or cable quality can all cause false triggers1.
Disadvantages of the DMX512 protocol also include its unidirectional transmission characteristics, which means that signals can only be transmitted in one direction and bidirectional communication is not possible. In addition, DMX512 does not include automatic error checking and correction functions, so special attention needs to be paid to issues such as electromagnetic interference and electrostatic discharge when connecting the controller to dimmers and special effects equipment to avoid false triggers