Take a look at the image below. It shows the basic communication locations used in Siemens PLC systems. This visual aid helps explain the different methods of communication that can be implemented with these controllers.
1. First, PPI Communication
PPI (Point-to-Point Interface) is the most fundamental communication method used by the S7-200 CPU. It allows communication through its built-in ports, either PORT0 or PORT1, and is the default setting for this type of PLC. It's widely used for simple data exchange between the PLC and other devices such as HMI screens or PCs.
2. Second, RS485 Serial Communication
RS485 serial communication is commonly supported by third-party devices. Siemens S7 PLCs can use the free port mode to communicate with external equipment like printers, inverters, or sensors. In basic applications, only the XMT (Transmit) instruction is needed to send data. However, more complex operations require custom programming within the PLC to handle both sending and receiving data.
When using the free port mode, users can control the communication port via instructions like XMT, RCV, and manage interrupts for transmission and reception, giving greater flexibility in handling serial communication tasks.
3. Third, MPI Communication
MPI (Multi-Point Interface) is a straightforward communication protocol used in Siemens PLCs. The speed of MPI communication ranges from 19.2 Kbit/s to 12 Mbit/s, making it suitable for medium-speed applications. It supports up to 32 nodes and has a maximum communication distance of 50 meters, which can be extended using repeaters—though each repeater also counts as a node.
MPI networks typically connect devices such as S7-200 PLCs, HMIs, programming tools, ET200S modules, and RS485 repeaters. Communication between Siemens PLCs can occur in three main ways: global data packets, non-configured connections, and configured connections.
4. Fourth, Ethernet Communication
Ethernet is a widely used networking technology that relies on a shared transmission channel. Its concept was first introduced in 1968 by the University of Hawaii and later developed into a personal computer LAN in 1973 by Metcalfe and Boggs. They named it "Ethernet," inspired by the idea of electromagnetic waves traveling through a hypothetical "ether."
In 1979, DEC, Intel, and Xerox standardized Ethernet, leading to its widespread adoption. Over time, various types of cabling were developed, including thin coaxial, twisted pair, and fiber optics. Ethernet offers high speed, easy setup, and robust network capabilities, making it ideal for industrial automation and control systems.
5. 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 communication, making it ideal for connecting PLCs with distributed I/O devices in industrial environments.
This protocol is particularly useful in applications where fast and reliable communication is essential, such as in process control, factory automation, and machine building. It ensures efficient data exchange between the central controller and remote peripherals.
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