Design of a LED display system with single-line serial communication

1 Introduction

At present, most large-scale LED display systems at home and abroad are basically composed of an LED control board and several LED unit boards connected in series.

The main body of the LED display system composed of the LED control board and the LED unit board is shown in Figure 1. Among them, the LED unit board includes a BUFFER circuit that enhances the signal driving capability, a decoding circuit that generates a dynamic display scanning timing, a number of switch tubes and a number of LED driving circuits. Its communication process is as follows: the communication signal sent by the LED control board is driven and enhanced by the BUFFER circuit of each serially connected LED unit board in turn; the scanning signal (SCANO) enhanced by the BUFFER circuit in each LED unit board is provided to the decoding circuit of this LED unit board, and the decoding circuit decodes to generate a dynamic display scanning timing control switch tube; the enable signal (ENO), latch signal (LATO), and clock signal (CLKO) enhanced by the BUFFER circuit in each LED unit board are respectively provided to all LED driving circuits in this LED unit board.

Figure 1 Commonly used LED display systems

The current LED display system has a display refresh frequency that is limited by the number of LED drive circuits and the communication speed of the LED drive circuits because the data signal passes through all the LED drive circuits on the LED unit boards that are connected in series. Most LED drive circuits use high-voltage, high-current, and large-size processes with strict cost control. The general communication speed does not exceed 30 MHz. When the display resolution is high, in order to ensure the display refresh frequency required for the display, the LED control board needs to send out multiple groups of communication signals to control multiple groups of LED unit boards that are connected in series. In most applications, dozens of control signals are often required, resulting in high production costs and complex application support, as shown in Figure 2.

Figure 2 Commonly used large-scale LED display systems

The new LED display system proposed in this paper is based on the single bus technology, one of the hot communication technologies today. It solves the communication and power supply problems through a single connection line, and has the advantages of simple structure, low cost, saving I/O port resources, and easy bus expansion and maintenance. This LED display system can effectively solve the above problems.

2 System Architecture and Communication Methods

2.1 System Architecture

This paper proposes a new LED display system with high communication speed, LED control board only needs to output one set of communication signals in most applications, low production cost and convenient application support. The system consists of an LED control board and several LED unit boards connected in series. The number of LED unit boards depends on the scale of the LED display system. The system is based on a single-line communication protocol, and the system architecture diagram is shown in Figure 3.

Figure 3 LED display system architecture

The LED unit board consists of an LED communication circuit, several switch tubes and several LED drive circuits. Among them, the LED communication circuit port includes a communication signal input terminal, a communication signal output terminal, a dynamic display scanning timing output terminal, a control signal output terminal and a data output terminal.

2.2 Communication Method

The LED control board sends a communication signal to the communication signal input end of the LED communication circuit on the first LED unit board, and the communication signal output end of the LED communication circuit of each subsequent LED unit board is connected to the communication signal input end of the LED communication circuit of the next LED unit board. The communication signal output end of the LED communication circuit of the last LED unit board is left floating or returned to the LED control board, forming the communication system of the LED display system described in this article.

Based on the LED display system architecture shown in Figure 2 and the communication system described above, the communication method is as follows:

The LED communication circuit is defined to include a communication signal input terminal, a communication signal output terminal, a dynamic display scan timing output terminal (SCAN<7: 0>), a control signal output terminal (En, Lat, Clk), and a data output terminal (DATAOUT); the communication signal is defined to include a communication signal output instruction, a dynamic display scan timing analysis instruction, a control signal timing control analysis instruction, and data; the LED communication circuit on each LED unit board analyzes the communication signal output according to the received communication signal and provides it to the communication signal input terminal of the LED communication circuit of the next LED unit board through the communication signal output terminal; the LED communication circuit of each LED unit board analyzes the dynamic display scan timing according to the received communication signal and controls the switch tube of the LED unit board through the dynamic display scan timing output terminal (SCAN<7:0>); the LED communication circuit of each LED unit board analyzes the control signal timing according to the received communication signal and controls the LED drive circuit of the LED unit board through the control signal output terminal (En, Lat, Clk); the LED of each LED unit board The communication circuit parses the data according to the received communication signal, and provides it to the data signal input of the first drive circuit of this LED unit board through the data output terminal (DATAOUT). The data signal output of each LED drive circuit of this LED unit board is connected to the data signal input of the next LED drive circuit. The communication signal output terminal of the LED communication circuit of the last LED unit board is left floating or returned to the LED control board.

The communication principle is that the system uses a set of serial frame data to represent the signals that need to be transmitted to each LED unit lamp driving circuit. The LED unit lamp driving circuit that receives these signals receives and processes the received data from the input frame data according to the communication mode and instruction type, constructs the processed data into new frame data as output, and sends it to the subsequent LED driving circuit with valid address according to the communication mode and instruction type to complete a communication. The method for the LED communication circuit to parse the received communication signal can adopt the method disclosed in the article "Single-line serial communication method for LED display system".

3 Conclusion

In the LED display system proposed in this paper, the data included in the communication signal only needs to pass through the LED communication circuit of each LED unit board connected in series, and then the data output end of the LED communication circuit controls the LED drive circuit on the LED unit board. The display refresh frequency is only limited by the number of LED unit boards and the communication speed of the LED communication circuit, thereby improving the communication speed by orders of magnitude. In most application scenarios, the LED control board only needs to output a set of communication signals to realize the control of the LED display system. The LED display system has the advantages of low production cost and convenient application support.