Research on LCD Display Based on Proteus

Proteus is an EDA tool software published by Labcenter electronics in the UK. It realizes the co-simulation from schematic design, code debugging to single-chip microcomputer and peripheral circuits, and switches to PCB design with one click, realizing the complete design from concept to product. It is the only design platform in the world that integrates circuit simulation software, PCB design software and virtual model simulation software. Its processor model supports 8051, HC11, PIC10/12/16/18/24/30/DsPIC33, AVR, ARM, 8086 and MSP430, etc. It can compile assembly language and support multiple compilers such as 1AR, Keil and MPLAB.
The software has rich resources, including component resources: thousands of simulation devices such as digital and analog, AC and DC, and more than 30 component libraries; instrument resources include: oscilloscope, logic analyzer, virtual terminal, SPI debugger, I2C debugger, signal generator, pattern generator, AC and DC voltmeter, AC and DC ammeter, etc.

1 128×64 dot matrix LCD
Currently, the commonly used dot matrix LCDs are 122×32, 128×64, 240×320, etc. There are three controllers for dot matrix LCD screens, namely KS0108, T6963C and ST7920. The main differences between the three controllers are: KS0108 does not have any font library, T6963C has ASCII code, and ST7920 has a national standard secondary font library (more than 8,000 Chinese characters).
Proteus's device library provides a variety of LCDs. This article takes the LCD controlled by the KS0108 controller as an example to study the display of the screen. There are two models of 128×64 dot matrix LCD screens controlled by the KS0108 controller in Proteus: LGM12641BS1R, AMPIRE 128×64.
1.1 LCD pins and function introduction
The pins and function introduction of 128×64 dot matrix LCD LGM12641BS1R and AMPIRE 128×64 are shown in Table 1.

As can be seen from Table 1, the main difference between LGM12641BS1R and AMPIRE 128×64 is the screen selection signal control terminals CS1 and CS2. LGM12641BS1R is high level valid, while AMPIRE 128×64 is low level valid. 1.2 LCD read and write timing
As shown in Figure 1, when the enable terminal E is high level and R/W is low level, the data DB0~DB7 is written and latched; when the read operation is E high level and R/W is high level, the latched data is read out and sent to the display.

2 LCD simulation in Proteus
2.1 Hardware circuit diagram
During the simulation process, the single-chip microcomputer 89C52 is used as the main control unit. Since two screens are controlled at the same time, in order to avoid confusion in the connection, the connection node mode is adopted, and "line marks" are added on the connection lines for corresponding connections. The overall circuit diagram is shown in Figure 2.

Since the effective levels of the screen selection signal control terminals CS1 and CS2 of LGM12641BS1R and AMPIRE 128×64 are different, inverters are added to the chip selection control terminals CS1 and CS2 of AMPIRE 128×64 to achieve synchronous display of the two. 2.2 Simulation steps
Since the LCD is a dot matrix type, to display Chinese characters, an auxiliary Chinese character modeling tool must be used. The author chose "Tsinghua Pengyuan's LCD character library display program". Pay attention to the settings of related items when taking the model, otherwise it cannot be displayed normally. The settings are shown in Figure 3.

When taking the modulus, the vertical modulus is adopted, and the bytes are reversed. The display effect is shown in Figure 4.
2.3 Program debugging
The program is written in C51 and debugged with Keil (if it is a program written in assembly language, the compiler that comes with the Proteus software can also compile it without Keil). During the debugging process, there is an option of "Options for Target + project name" in the Project. Click "Output" and put a check mark in front of "Create HEX Fi" to indicate that it is selected. In this way, in the Proteus ISIS simulation environment, you can directly load the *.hex file generated in Keil for simulation demonstration.

3 Conclusion
Taking the two LCDs, LGM12641BS1R and AMPIRE 128×64, controlled by two KS0108 controllers driven by 89C52 as an example, the precautions for simulation and the effects of simulation are given. For the simplicity of the circuit, the node method is used for connection, and the line mark is added on the connection line to achieve the connection. Of course, the bus method can also be used. Proteus is widely used in the field of single-chip microcomputer simulation. It not only supports the 8051 series CPU model, but also supports the 68000, AVR, PIC12, PIC16, PIC18, Z80, HC11 and other series of single-chip microcomputers. It can also simulate analog circuits, digital circuits and mixed circuits of the two. Software simulation saves consumables, improves efficiency, simplifies the design process, and is worthy of widespread use.