Summary of Five Core Communication Methods for Siemens PLC

Siemens, as one of the earliest industrial control manufacturers to enter the Chinese market, has maintained a very high market share.

Siemens PLCs have excellent quality, and their network stability and openness are favored by industrial control personnel. Moreover, the variety of programming software is convenient to use, making it prominent in the domestic industrial control field.

Although everyone has some understanding of Siemens PLCs, if asked to describe the characteristics of various communication methods of Siemens PLC, many people might struggle to give a complete answer. Below, we will introduce several common Siemens communication methods!

PPI protocol is the most basic communication method for the S7-200 CPU, which can communicate through its own ports (PORT0 or PORT1). It is the default communication method for the S7-200 CPU.

Most third-party devices support this, and Siemens S7 PLC can control serial communication by selecting a free port communication mode. The simplest case is to send commands (XMT) to third-party devices like printers or inverters. Regardless of the situation, programming must be done through the S7 PLC.

When the free port mode is selected, users can control the communication port operations by sending commands (XMT), receiving commands (RCV), sending interrupts, and receiving interrupts.

MPI communication is a relatively simple communication method, with an MPI network communication rate of 19.2Kbit/s to 12Mbit/s, supporting up to 32 nodes with a maximum communication distance of 50M. The communication distance can be extended through repeaters, but repeaters also occupy nodes.

MPI network nodes can typically include S7-200, human-machine interfaces, programming devices, intelligent ET200S, and RS485 repeaters.

There are generally three communication methods between Siemens PLCs using MPI:

1. Global Data Packet Communication Method

2. Unconfigured Connection Communication Method

3. Configured Connection Communication Method

The core idea of Ethernet is to use a shared public transmission channel, which originated at Xaverian College as early as 1968. In 1972, Metcalfe and David Boggs (both renowned networking experts) set up a network that connected different ALTO computers and also connected EARS laser printers.

This was the world’s first personal computer local area network, which first operated on May 22, 1973. On that day, Metcalfe wrote a memo suggesting the network be renamed to Ethernet, inspired by the idea that “electromagnetic radiation can be transmitted through luminous ether.” In 1979, DEC, Intel, and Xerox standardized the network.

In 1984, thin cable Ethernet products emerged, followed by thick cable, twisted pair, CATV coaxial cable, fiber optic cables, and various mixed Ethernet products. Ethernet is currently one of the most popular topology standards in the world, offering high transmission rates, abundant network resources, robust system functions, simple installation, and easy maintenance.

PROFIBUS-DP fieldbus is an open fieldbus system that complies with European and international standards.

PROFIBUS-DP communication features a very streamlined structure, with high and stable transmission speeds, making it suitable for communication between PLCs and distributed field I/O devices.