Application of ST7920 controller in small and medium size LCD

Crystal oscillator
Crystal resonator 2.5*2.0mm 2520 16MHZ (16.000MH
Photocoupler

1 Introduction

LCD liquid crystal display devices are widely used in the interface of human-computer interaction of instrumentation because of their low voltage, low power consumption, large display information and long service life. At present, with the rapid development of integrated circuit manufacturing technology and electronic technology, LCD devices have become one of the most important information processing methods in the information industry. At the same time, more and more portable digital devices used in many fields of application use the microcontroller as the control core and the LCD as the display terminal. The 12864 dot matrix liquid crystal is a typical representative of small and medium size liquid crystals, and is widely used. This article takes ST7920 as the controller's 12864 as an example to introduce its practical application method.

2.ST7920 is an introduction to the controller 12864

2.1 LCD display control instructions

In order to display information, the LCD needs to write the displayed encoded data into the LCD display buffer. The data writing can be completed by a series of liquid crystal display control commands.

The ST7920 control signals RS and R/W control the display control commands. DB0-DB7 is a data bus that implements data communication between the external CPU and the internal processor of the liquid crystal. The interactive data includes control commands and data to be displayed. The main instruction list of the 12864 Chinese character library dot matrix screen liquid crystal display control based on ST7920 controller is shown in Table 1.

2.2 LCD display control timing

As with other controllable devices, a certain control timing is required for the liquid crystal cell to work properly. The so-called timing is the sequence of matching the high and low levels of the control signal. For LCD driver development, the host controller must communicate with the ST7920 controller in accordance with the appropriate timing. Figure 1 is a timing diagram of an 8-bit parallel port write operation for the 12864 liquid crystal controlled by the ST7920. It can be seen from Fig. 1 that when the write operation control is performed through the 8-bit parallel port DB0-DB7, three control signals of RS, R/W, and E are required to cooperate. First, the RS is based on whether the data written on the parallel port is a control command or a display data. Set or set to 0, secondly, the R/W read/write control signal needs to be set to 0 after the write operation, and then the control enable signal E should be set to 1. After only the above three control signals are stabilized, the 8-bit parallel port can be DB0-DB7. The data on the bus can be written to the LCD screen. After the writing is completed, the enable signal E is set to 0. In the use, pay special attention to the unstable phase during the high and low level conversion of each control signal, and read and write operations should try to avoid this. One stage. The ST7920 controlled 12864 LCD 8-bit parallel port read operation timing diagram is similar to the write, except that the read and write control signals are different.

3. Liquid crystal display hardware interface circuit

The following takes the STC89C52 single-chip microcomputer to control the liquid crystal display as an example to introduce the connection method between the MCU and the liquid crystal. Figure 2 is an 8-bit parallel port STC89C52 control interface diagram. The P1 port of the MCU is connected to the DB0-DB7 of the liquid crystal as a bus channel for command and display data; P3.0, P3.1, and P3.2 are respectively connected to the RS, R/W, and E of the liquid crystal to form a liquid crystal display control signal. Channel.

4. Liquid crystal display software design

According to the hardware connection diagram of FIG. 2, the program code is designed by taking a character such as "ST7920 display control" on the liquid crystal screen as an example.

5. Conclusion

Small and medium-sized liquid crystal displays have become more and more widely used as human-computer interaction interfaces for electronic devices due to their own advantages. This paper introduces the hardware and software implementation method of the 12864 small and medium size liquid crystal display of the controller of ST7920 and the development and use steps of the liquid crystal display application. The method has certain universal applicability and provides certain reference for designing other forms of liquid crystal display.

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