Introduction to the communication methods of mainstream PLC equipment abroad

1. Rockwell ABRockwell's PLCs mainly include: PLC2, PLC3, PLC5, SLC500, ControlLogix and other models. PLC2 and PLC3 are early models. The most commonly used small PLCs are SLC500, medium-sized ones are generally ControlLogix, and large ones use PLC5 series. DF1 protocol is a communication protocol supported by all Rockwell PLCs. DF1 protocol can transmit data through serial media such as 232 or 422, or through network media such as DH, DH+, DH485, ControlNet, etc. The specific content of DF1 protocol can be downloaded from AB's database. AB's PLC also provides OPC and DDE. Its integrated software RSLogix includes DDE and OPC SERVER, and data communication can be carried out through the above software. AB's mid-to-high-end PLCs also provide high-level language programming functions, and users can also implement their own communication protocols through programming.

Second, GE's 90-70 and 90-30 series PLCs are currently used more in China. Both PLCs support the SNP protocol, and the specific contents of the SNP protocol are in its PLC manual. Now GE's PLCs can also be linked via Ethernet. The contents of GE's Ethernet protocol are not open to the public, but GE provides an SDK development kit, which can be used for communication.

3. Siemens PLC series mainly include its early S5 and current S7-200, S7-300, S7-400 and other models of PLC. The early S5PLC supports the 3964R protocol, but because it is less used in China now, except for very few transformation projects, there are few data communications with it. S7-200 is a small Siemens PLC. It has been widely used in China because of its low price. It supports MPI, PPI and free communication port protocols. Siemens 300 PLC supports MPI, and can also communicate with computers through Profibus and industrial Ethernet bus systems. If you want to complete point-to-point communication, you can use CP340/341. As a large Siemens PLC, S7400 provides quite complete communication functions. You can communicate through the S7 standard MPI, and you can also communicate through C-bus, Profibus and industrial Ethernet. If you want to use point-to-point communication, S7-400 needs to use the CP441 communication module. Siemens' communication protocol is not public. Many configuration software support MPI, PPI and other communication methods. Profibus and Industrial Ethernet generally communicate data through Siemens software.

4. Schneider (Modicon) Schneider has many PLC models and they are widely used in China. Its communication methods mainly support two communication protocols: Modbus and MODBUS PLUS. The Modbus protocol has been widely used in the industrial control industry. It is not only a PLC communication protocol, but also widely used in many intelligent devices such as intelligent instruments and frequency converters. After further development, MODBUS now has the MODBUS TCP method, which transmits through Ethernet and has a faster communication speed. Compared with MODBUS, Modbus PLUS has a faster transmission speed and a longer distance. This communication method requires the installation of the SA85 card provided by MODCON on the computer and the installation of the card driver before communication can be carried out. In addition to the above two methods, Modicon's PLC also supports multiple communication methods such as TCP/IP Ethernet, Unitelway, FIPWAY, FIPIO, AS-I, Interbus-s, etc.

5. Omron series PLCs are also widely promoted in China. In terms of communication methods, OMRON currently mainly uses two communication methods: Host Link protocol is a communication method based on serial port for data transmission. When the PLC enters the MONITOR mode, the host computer can communicate with the Omron PLC. When communicating with Omron, please note that a certain amount of time should be left between two communications. If the communication speed is too fast, it is easy to cause PLC communication abnormalities. ControlLink is a fast communication method for Omron PLC. Control Link communicates data through boards. There is a data exchange area between boards. The boards realize data exchange and complete the data acquisition function. To use this communication method, you need to configure the Omron driver.

6. Mitsubishi PLC's small PLC is widely used in China. Mitsubishi has many PLC models, mainly including FX series, A series and Q series. Mitsubishi series PLC has many communication protocols, and each series has its own communication protocol. For example, the FX series includes communication through the programming port or 232BD, and can also communicate through 485BD and other methods. Its A series and Q series can communicate through Ethernet. Of course, Mitsubishi's PLC can also communicate through the CC-LINK protocol.

7. The Panasonic PLC and computer can communicate through serial port and Ethernet. The communication protocol adopted is MEWTOCOL protocol. Like most Japanese PLCs, MEWTOCOL protocol is relatively simple. Many software can read data directly from PLC.

The above is the mainstream PLC equipment communication method introduced abroad. In addition to the above manufacturers, there are many other PLC manufacturers: Manufacturer Model Protocol Medium LGSTER-K10S/30S/60S/80S/K200 SMASTER-K Serial Port Hitachi H Series EH150, etc. Hi Protocol Serial Port/USB Guangyang All Series CCM2 Protocol Serial Port Xinjie All Series Modbus Serial Port Kaidian All MODBUS Serial Port

The author believes that it is difficult for PLCs on the market to integrate. The main reason is that they lack a common communication language, which directly limits the pace of PLC development. The communication between PLC and host computer is also due to the inconsistency of PLC communication protocols of various manufacturers. When we do network communication, we are often hindered by a large number of communication protocol message formats. The emergence of OPC protocol specifications has broken this situation. However, to completely solve the communication between PLCs of different brands, it is not enough to rely on a technical specification. I believe that in the future, PLCs will definitely be compatible with a specified communication protocol.