Each scanning board is responsible for controlling several lines (columns) on the LED display screen, and the display and control signals of the rental screen of the LED display screen on each row (column) are transmitted in series.The main control box obtains the luminance data of a screen pixel from the display card of the computer, and then redistributes it to several scanning boards.
1、 Pulse width modulation. The content of scanning board serial transmission is not the switch signal of each LED display screen, but an 8-bit binary gray value. Each LED has its own pulse width modulator to control the lighting time. In this way, in a repeated lighting cycle, each pixel only needs 4 pulses at 16 gray level and 8 pulses at 256 gray level, which greatly reduces the serial transmission frequency. With this method, 256 gray levels can be easily controlled.
2、 The scanning board controls the gray level of each pixel in a centralized way. The scanning board differentiates the gray value of each line of pixels from the control box (i.e. pulse width modulation), and then transmits the registration signal of each line of led to the corresponding LED in the form of pulse (lit as 1, not lit as 0) in a serial way to control whether it is on or not. This method uses less equipment, but the amount of serial transmission data is large, because in a repeated lighting cycle, each pixel requires 16 pulses at 16 levels of gray level, and 256 pulses at 256 levels of gray level. Due to the limitation of equipment operation frequency, the LED screen can only achieve 16 gray levels.