Abstract: On the basis of comprehensive analysis of many design schemes of control circuit in LED large-screen display system design, the implementation methods of different design schemes with single-chip microcomputer, programmable logic device and embedded computer technology as control core are given respectively. The characteristics of these several programs were compared and the application was introduced.
LED dot matrix is ​​an important display terminal for public information, and large-screen LED dot matrix display screens can be applied in many occasions. Large-screen display technology is more difficult to display than small and medium-sized screens, because its screen is large, the number of LED points is large, and each point is refreshed in a very short time, which requires that the scanning rate must be very high, in addition, the large screen as information The important media released have high requirements for stability, reliability and scalability. Only well-designed control circuits can meet the above requirements. This article focuses on several design methods for control circuits in LED large-screen design, and gives different solutions for different design requirements.
1 LED large screen system works
A typical LED large-screen display system is mainly composed of a signal control system, a scanning and driving circuit, and an LED array. The system structure is shown in FIG. At present, the screen design of most LED displays adopts a modular structure, and its basic unit is an LED display unit module, the screen size and shape can be flexibly changed, and the display installation and maintenance are also very convenient.
Figure 1 System block diagram
The signal control system is a microcomputer system, a single chip system, a microcomputer Z single-chip master-slave control system, a programmable logic device control system, an infrared remote control system, a paging receiving and control system, and the like. The task of the signal control system is to generate or receive the digital signals required for LED display and to control the various components of the entire LED display system to work in accordance with a certain division of labor and timing. The row driver circuit is mostly a triode array, which supplies a large current to the LED. The column drive consists of a serial-in and parallel shift register and a latch (or a shift register with a latch function).
After the data to be displayed is ready, the control system first sends the first row of data into the shift register and latches, and then the row scan circuit strobes the first row of the LED array, after lighting for a period of time, then displays the subsequent row in the same manner. Until the display content of one frame is completed, this cycle is repeated. According to the principle of persistence of vision, it is possible to achieve 24f/s display so that the naked eye has no obvious pause, which is equivalent to the response time of 40ms or less. When the LED display screen is large in area, the amount of data transmitted is also very large, thereby increasing the response time of the display system to cause flicker, and in order to improve the visual effect, the parallel display can be performed in sections.
In the high-speed dynamic display, the luminance of the LED is proportional to the illumination time in the scanning period, so the gray scale display can be realized by modulating the ratio of the illumination time of the LED to the scan period (ie, the duty ratio).
2 LED large screen control circuit design
The design of the control circuit is the core of the large-screen system design. The control circuit design includes the design of the signal control system, the scanning circuit and the driving circuit. The design of the control circuit is generally controlled by data memory, data buffer, counter, synchronous controller, and read/write control. , master-slave controller, address controller, frame memory, data selector, gray modulator, shift register, etc. At present, LED display control circuit design widely uses two types of devices as its control core to achieve, one is the single-chip control system, and the other is the programmable logic device.
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