Design of LED display control circuit based on CPLD

Introduction: in recent years, with the rapid development of computer technology and integrated circuit technology, large screen display system which is widely used is the video LED display system. In the LED display technology, the red and green LEDs brightness, color light effect etc. the performance has been greatly improved, and the development of computer multimedia software, now the pseudo color LED video display system can greatly reduce the manufacturing cost, applications continue to increase. The pseudo color LED video display system using the computer multimedia technology, the synchronous dynamic display of video images, clear image, high brightness, no seams, video gradation of each color is from the early 16 level rise now 256 gray, with the development of large scale integrated circuit and special components, full color video LED 256 gray scale display system are possible at any time. With the rapid development of LED electronic display technology, it has become one of the leading technologies in the field of flat panel display. This paper introduces the design of LED display control circuit with M4A5-128P64-10VC.

1, LED display structure

In the LED display system, the lattice structure unit is the basic structure. Each display driving unit is composed of a plurality of 8 * 8 dot matrix LED display modules. A plurality of display driving boards are assembled together to form a display screen with a plurality of square meters, which can be used for displaying various words and images. LED display screen, including computer video capture circuit, control circuit, drive circuit and power supply, as shown in figure 1. LED display with red, green two kinds of primary colors, each of the basic colors of the gray level of 256, the pixel pitch of 7.62mm, pixels in the horizontal direction of up to 1024 points, the vertical direction can be up to 768 points.

2, LED electronic display features

The LED display is composed of a plurality of display unit spliced, the display mode of using the principle of LED dot matrix display screen and computer mapping, a pixel is LED dot matrix corresponds to a pixel of the computer display screen, such as a computer screen according to the resolution is divided into 640 columns and 480 rows, i.e. the LED display 640 * 480 dot matrix unit, each lattice unit also includes red, green and blue three kinds of light emitting diode, the three light emitting diode emits three color light color is obtained after the human eye feeling color, three color according to the optical principle, we only collected on the computer screen every point of the image digitized and decomposed into red, green and blue three kinds of signals through the system after the transfer to the lattice unit of LED dot matrix screen, respectively corresponding to the light emitting diode driving color, i.e. The computer screen on the LED dot matrix screen.

3, LED electronic display driver

In most of the LED display system, the refresh drive method of each LED display drive unit column store data to lock in to scan, according to the LED display driver board structure, the 1P16 scanning duty ratio. We have designed the LED display driver board drive circuit of 4:16 line decoder with two 74HC595, it provides the whole scanning circuit for signal, but also uses the 74HC595 chip to make the serial shift register, it will be the serial data from the system shift into parallel signal output, thus driving the column needs to provide the serial clock, shift the parallel locking signal and an output enable signal for scanning to serial data input and serial clock signal, as shown in figure 2. Therefore, we need to design a timing control circuit.