As one of the earliest industrial control manufacturers to enter the Chinese market, Siemens has maintained a strong and dominant market position for many years. The quality of Siemens PLCs is widely recognized, with their network stability and open architecture making them a popular choice among industrial automation professionals. Their programming software is well-organized and user-friendly, which has helped Siemens establish a solid reputation in the domestic industrial control industry.
Although many people are familiar with Siemens PLCs, not everyone may be fully aware of the various communication methods that Siemens offers. In this article, we will explore some of the common communication protocols used by Siemens PLCs and explain their features and applications.
First, PPI Communication
PPI (Point-to-Point Interface) is the most basic communication method used by the S7-200 CPU. It allows communication through its built-in ports (PORT0 or PORT1), and it is the default communication protocol for the S7-200 series. This method is commonly used for simple data exchange between the PLC and other devices.
Second, RS485 Serial Communication
RS485 is a widely supported communication standard, and Siemens S7 PLCs can use the free port mode to communicate with third-party devices. In the simplest scenarios, the S7 PLC can send commands using the XMT (Transmit) instruction to devices like printers or inverters. However, this type of communication always requires custom programming to handle the specific requirements of each device.
When using the free port mode, users can control the communication port by using instructions such as XMT (Transmit), RCV (Receive), and by managing transmit and receive interrupts.
Third, MPI Communication
MPI (Multi-Point Interface) is a relatively straightforward communication method. It supports communication speeds ranging from 19.2 kbit/s to 12 Mbit/s, and it can connect up to 32 nodes over a maximum distance of 50 meters. With the help of repeaters, the communication distance can be extended, although each repeater also occupies one node.
MPI networks are often used to connect various components such as S7-200 PLCs, HMI devices, programming tools, intelligent ET200S modules, and RS485 repeaters.
There are three main ways to implement MPI communication between Siemens PLCs:
1. Global Data Packet Communication
2. Non-Configured Connection Communication
3. Configured Connection Communication
Fourth, Ethernet Communication
Ethernet is a core concept in modern networking, originally developed at Xerox PARC in 1968. In 1972, Robert Metcalfe and David Boggs created the first local area network (LAN) connecting multiple ALTO computers via an EARS laser printer. This was the world’s first personal computer LAN, launched on May 22, 1973.
Metcalfe later proposed the name "Ethernet," inspired by the idea of electromagnetic waves traveling through a theoretical medium called "ether." In 1979, DEC, Intel, and Xerox standardized the Ethernet protocol, leading to its widespread adoption.
Over time, Ethernet evolved to support various physical media, including thin coaxial cable, twisted pair, fiber optics, and more. Today, Ethernet remains one of the most popular and versatile networking standards due to its high speed, rich resources, and ease of installation and maintenance.
Fifth, PROFIBUS-DP Communication
PROFIBUS-DP is an open fieldbus system that adheres to European and international standards. It is known for its compact structure and high-speed, stable transmission, making it ideal for communication between PLCs and distributed I/O devices in industrial environments.
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