Design of LED display screen control system based on LPC2210

With the development of computer and semiconductor technology, LED large-screen display system has become a display device integrating computer control, video, optoelectronics, microelectronics, communication, and digital image processing technology. With the development and progress of large-screen display technology, the data that needs to be processed has increased significantly, the system frequency is higher and the scale is larger, and the requirements for display control systems are also increasing. At present, LED displays often use 8-bit/16-bit microprocessors. Due to their operating speed, addressing capability and power consumption, they are difficult to meet relatively complex applications with large display areas and frequent display content switching. There are many problems such as large system size, difficult debugging, difficult to modify, and unstable system. ARM has the characteristics of small size, low power consumption, and strong data processing capability. In an independent display system without computer support, it is an ideal solution to use an embedded system to solve many requirements for information display. Therefore, this design uses the LPC2210 microprocessor as the core of the control circuit to solve the problems of system operating speed, addressing capability and power consumption, thereby supporting stable display of a larger visual area and storing more display content.

1 System Hardware Composition and Principle

This system uses the LPC2210 microprocessor produced by Philips, and uses the low-power, low-cost ARM7TDM I as the core system hardware. The system is mainly composed of display control circuit and LED display screen, as shown in Figure 1.

The control circuit with ARM7 (LPC2210) microprocessor as the core mainly completes the data conversion signal control work. The scanning drive circuit of the LED display mainly uses 74HCl38 and 74HC595 to complete the row scanning and complete the column control by controlling the timing. The display screen uses LED as pixels and is spliced ​​by LED dot matrix display units. The display screen designed in this design has a dot matrix structure of 16 rows × 64 columns.

In the design, the 16 pins of LPC2210P0 port are used as the interface of the display control circuit, and they correspond to the screen enable terminal EN, row selection signal terminal (A, B, C, D), row lighting data signal terminal (GD1, GD2, RD1, RD2) and two timing signals LAT, CLK, etc.

2 System Software Design

Since the display control circuit of this LED display mainly uses 74HCl38 and 74HC595 to complete row scanning and column control by controlling the timing, and these timings are completed by the software part, the reasonable design and implementation of the timing logic should be considered first in the design of the software system. In this LED display, two timings are required, namely the cache timing CLK to complete the data cache and the screen timing: LAT to light up the cached data. After the rising edge of CLK appears, the data is stored in the cache of the screen in sequence. After the rising edge of LAT appears, the screen sends the cache content to a certain row of the screen. In addition, the selection of rows during row scanning, as well as the display module, communication module, screen clearing module, etc., the writing of sub-modules and the coordinated use of each sub-module should also be considered.

It should be pointed out that in order to improve the scalability of the LED display, the system will inevitably increase the frequency requirements. For this reason, in the design process of the system software, this design uses the phase-locked loop (PLL) built into the LPC2210 microprocessor to multiply the system frequency to improve the scalability of the system. The system software architecture design is shown in Figure 2.

2.1 PLL module

The input clock frequency range of the LPC2210 PLI is 10 to 25 MHz. 11.0592 MHz is selected as the external crystal frequency of the system. First, the PLL needs to be configured. The calculation formula is shown in formula (1).

Among them, Fosc is the crystal frequency, Fcco is the frequency of the PLL current controlled oscillator, cclk is the output frequency of the PLL, that is, the clock frequency of the processor, and M and P are the multiplier value and divider value of the PLL respectively.

The CCO frequency can be obtained by formula (2).

The source code of the PLL module is as follows:

2.2 Other main modules

Mainly completes the line scanning and the scanning module of each point in the line

3 System Verification

Using ADS1.2 for online simulation verification, through the design of hardware and the coding and debugging of software code, the dot matrix LED screen has realized the function of displaying various information in a dual-color and diversified way, and the display screen can be expanded through simple cascading. And a comparative analysis was conducted in two cases, without calling the PLL module and calling it, and a relatively obvious phenomenon was obtained, that is, when the PLL module is called, the system display is more stable and more suitable for the expansion of the dot matrix LED screen.

4 Conclusion

This design uses the 32-bit ARM embedded microprocessor LPc2210, adopts an expandable and modular design, with the display circuit of the LED screen and the ARM microprocessor control circuit as the core, to realize the function of the dot matrix LED screen to display various information in a dual-color and diversified manner. At the same time, the display screen can be expanded through simple cascading, solving the problems of system operation speed, addressing capability and power consumption.