introduction As the focus of the development of production process automation, fieldbus plays a huge role in promoting automation technology and is a symbol of modern industry. As a communication protocol of field bus, MODBUS realizes communication and information exchange between PLC controller, industrial control instrument and equipment. Although industrial control instruments with MODBUS function are widely used, industrial control instruments and PLC controllers are relatively expensive and have not formed products with independent intellectual property rights, which hinders its further development. This article starts with this problem and designs a single-chip microcomputer control system based on the MODBUS protocol . The design is reasonable, the price is low, and the autonomy is strong. It has a wide application prospect in the field of industrial control. 1 Overall system design In the system, the computer PC is used as the host, and the AVR single-chip microcomputer is used as the slave, which uses RS-485 industrial field bus communication. Because the serial port of the computer adopts the RS232 bus standard, the RS485-RS232 level converter must be added to the serial communication port of the host computer, and the RS-232 level and RS-485 level are realized by the level converter at the serial port of the computer Conversion, the host and the slave communicate and exchange data on the RS-485 bus through the MOD-BUS communication protocol, and up to 255 slaves can be connected on the entire RS-485 bus. The overall structure of the system is shown in Figure 1. The entire hardware circuit includes: PC, RS485-RS232 level converter, power supply, reset circuit, crystal oscillator circuit, AVR microcontroller control system. The upper computer of this system is composed of PC and serial port, and the lower computer is composed of two single-chip microcomputer control systems. The addresses of the two slave devices are 01 and 02. Each MCU system consists of Atmega32 MCU, TSl2864A-3 LCD liquid crystal display, sensor, and PWM pulse width modulation control circuit. The lower computer is based on the Atmega32 single-chip computer, and the data collected by the sensor is then displayed on the LCD screen after A / D conversion. The Atmega32 single-chip computer has a MAX485 serial port and communicates with the upper computer through the RS-485 bus. The overall hardware schematic of the system is shown in Figure 2 As shown. Our company is specialized in supplying high quality Capillary Tube.Capillary Copper Tube are critical parts used as restrictors against refrigerant flow and pressure in the refrigeration cycle of air conditions, electric refrigerators, showcases freezer, this copper tubing usually manufactured with fine precision, down to one thousandth of an inch. This precision allows airflow to be smoother, more uniform, and more closely monitored, making such applications as fluid & air restrictors much more useful. Capillary copper tubing has very small inside diameters.Production Standard: ASTM B280, ASTM B360 JISH3300 .etc.Our parts have been exported to over 50 countries all over the world. Capillary Tube Capillary Tube,Copper Capillary Tube,Air Conditioning Capillary Tube ZHEJIANG ICE LOONG ENVIRONMENTAL SCI-TECH CO.,LTD. , https://www.ice-loong.com
2 System hardware design 