In the vast realm of industrial control, Siemens stands out like a brilliant star. As one of the earliest industrial control manufacturers to enter the Chinese market, it maintains a formidable market share. Its PLC products attract the attention of many industrial control professionals with their exceptional quality, stable networks, and open compatibility, much like a magnet. The richness and convenience of its programming software further enhance its appeal. However, do you truly understand the mysterious and powerful communication methods of Siemens PLC? Now, let us unveil them together.
1. PPI Communication, is the most basic communication method for the S7-200 CPU, acting like a loyal guardian. Through its built-in ports (PORT0 or PORT1), it quietly protects the default communication channel of the S7-200 CPU. It serves as a dedicated information pathway, facilitating initial communication between devices in a simple and pure manner.
2. RS485 Serial Communication resembles a grand party with third-party devices. Most third-party devices welcome it with open arms, and the Siemens S7 PLC can easily take control of the serial communication stage by selecting the free port communication mode. The simplest scenario is akin to an elegant messenger, merely sending commands (XMT) to transmit information to third-party devices such as printers or inverters. However, in any case, the S7 PLC, as the clever “director,” must write the program to orchestrate this communication “drama.” When the free port mode is selected, the user wields a magical wand, effortlessly controlling the communication port’s every move through sending commands (XMT), receiving commands (RCV), sending interrupts, and receiving interrupts.
3. MPI Communication is like an elegant socialite, actively participating in communication with a relatively simple approach. Its communication speed gracefully dances between 19.2Kbit/s and 12Mbit/s, and the MPI network can enthusiastically accommodate up to 32 nodes, with a maximum communication distance of 50M. It seems to possess long arms and can further expand its “social circle” through repeaters, although repeaters will occupy one node position. MPI network nodes resemble a lively gathering place, typically including S7-200, human-machine interfaces, programming devices, intelligent ET200S, and RS485 repeaters among its network components. The MPI communication between Siemens PLCs is like a meticulously choreographed dance, featuring three elegant “dance steps”: global data packet communication, unconfigured connection communication, and configured connection communication.
4. Ethernet Communication has a legendary background. Its core idea originated from a spark of inspiration at Stanford University in 1968, and in 1972, Metcalfe and David Boggs built the world’s first personal computer local area network, marking a significant moment of birth. On May 22, 1973, when it first operated, Metcalfe’s memo bestowed upon it the poetic name “Ethernet.” In 1979, DEC, Intel, and Xerox standardized it, and thus it embarked on a journey to global popularity. Since 1984, various Ethernet products have emerged like stars, and today it has become one of the most popular topological standards in the world. With high transmission rates, abundant network resources, powerful system functions, simple installation, and convenient maintenance, it shines brightly in the field of industrial control.
5. PROFIBUS-DP Communication is like an efficient and pragmatic worker. As an open fieldbus system, it strictly adheres to European and international standards. Its communication structure is as simple as a precise surgical knife, yet its transmission speed is as fast and stable as a running cheetah. This characteristic makes it an ideal choice for communication between PLCs and distributed I/O devices in the field, serving as a tightly connected link that ensures efficient data transmission.
In summary, these common communication methods of Siemens PLC each have their unique strengths. PPI communication is the foundational communication path for the S7-200 CPU; RS485 serial communication excels in interacting with third-party devices and requires program direction; MPI communication is simple and can connect multiple nodes, offering various communication methods between PLCs; Ethernet communication has a long history and numerous advantages; and PROFIBUS-DP communication is specifically designed for communication between PLCs and field I/O devices. Understanding the characteristics of these communication methods is like possessing a key that unlocks the door to the efficient application of Siemens PLC, allowing us to navigate more freely in the ocean of industrial control.
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