Design of LED display system based on CH451 chip

0 Introduction

LED dot matrix display is a new display method that integrates microelectronics technology, computer technology, and information processing. Due to its advantages such as long life, wide dynamic range, stable and reliable operation, low power consumption and fast time response, it has become a leader among many display media and an ideal choice for outdoor work display. The use of CH451 chip to drive LED dot matrix has the following characteristics: fast speed, low power consumption, dynamic display scanning control, direct drive of 64-bit LED dot matrix, and software control of LED brightness to reduce power consumption. CH451 can exchange data with controllers such as single-chip microcomputers through a 1-wire or cascaded 4-wire serial interface. The serial interface of CH451 is implemented by hardware, and the controller can frequently perform high-speed operations through the serial interface without reducing the working efficiency of CH451. The circuit designed with it not only has simple software and hardware design, but also has low power consumption, fast response speed, strong driving ability, and fewer I/O port lines occupied. It is a cost-effective and flexible design solution.

1 Instructions for use of CH451

CH451 has 8 8-bit data registers inside, which are used to store 8 word data, corresponding to 8 groups of 8 light-emitting diodes driven by CH451, and supports left shift, right shift, left cycle, right cycle of word data in data register, and supports independent flashing control of each digital tube. In the process of left-right shift or left-right cycle of word data, the properties of flashing control are not affected. CH451 has a hardware-implemented high-speed 4-wire serial interface, including 4 signal lines: serial data input line DlN, serial data clock line DCLK, serial data load line LOAD, serial data output line DOUT. DIN is used to provide serial data, high level indicates bit data 1, low level indicates bit data 0, and the order of serial data input is low bit first, high bit last. DCLK is used to provide serial clock, CH451 inputs data from DIN on its rising edge and outputs data from DOUT on its falling edge. CH451 has a 12-bit shift register inside. At the rising edge of DCLK, the bit data on DIN is shifted into the highest bit register of the shift register. Similarly, the original second lowest bit data is shifted into the lowest bit register. At the first falling edge after the rising edge, the original second lowest bit data is output from DOUT. CH451 allows the serial clock frequency of the DCLK pin to be greater than 10MHz, so that high-speed serial input and output can be achieved. LOAD is used to load serial data. CH451 loads the 12-bit data in the shift register at its rising edge and analyzes and processes it as an operation command. CH451 can dynamically drive 8×8 LED dot matrix. All columns of the dot matrix are connected to the column drive pins SEGO~SEG7 of CH451 through the series current limiting resistor R1, and all rows of the dot matrix are driven by the DIG0~DIG7 pins of CH451 respectively. The larger the resistance of the series current limiting resistor R1, the smaller the segment drive current and the lower the display brightness of the digital tube. The resistance of R1 is generally between 60Ω and 400Ω. Under the same other conditions, a larger resistance should be selected.

2 Software and Hardware Design Examples

2.1 Hardware Circuit

Figure 2 is a display panel circuit designed using AT89C52 and CH451 interface.

P1.5, P1.6, and P1.7 of the Pl port are used to control the display of the LED dot matrix, and are connected to the LOAD, DIN, and DCLK pins respectively. Four 8×8 LED arrays form a 16×16 dot matrix screen module. If you want to display a Chinese character, just send the 32-byte dot matrix data to CH451 through eight 48-bit load word data commands. Because there are four CH451 cascades, each operation command must be 48-bit data, and finally the LOAD signal line outputs a rising edge to notify all CH451 to load their own command data.

2.2 Display Driver

Define an array to store display data. After the CPU is reset, call the CH451 Write function to write commands and data to CH451.

Write 12bit control word function:

3 Conclusion

From the above examples, we can see that using CH451 to design LED dot matrix drive circuit does not involve complicated technical problems in hardware and software design, especially software design. This is a solution when I/O lines are tight. It has a good cost-effectiveness.