Established in 1847, Siemens, a renowned company, has consistently maintained a dominant market share. The quality of Siemens PLC is exceptional, cherished by industrial control professionals for its network stability, openness, and diverse programming software categories that facilitate user-friendly operation. It holds a prominent position in the field of industrial control.
While many have a general understanding of Siemens PLC, articulating the distinctive features of its various communication protocols may challenge most. Let's delve into some common Siemens communication protocols to shed light on their unique characteristics!
1.PPI protocol
The PPI protocol stands as the fundamental communication method for the S7-200CPU, operating seamlessly through its native ports (PORT0 or PORT1). It serves as the default communication mode for the S7-200CPU, offering straightforward connectivity.
2.RS485 communicatio
RS485 serial communication is widely supported by third-party devices. Siemens S7 PLCs can control serial communication by selecting the Freeport communication mode. In its simplest form, sending commands (XMT) is used to transmit information to third-party devices such as printers or variable frequency drives. Regardless of the scenario, programming through S7 PLC is essential for implementation.
When opting for the Freeport mode, users can control the operation of the communication port by sending commands (XMT), receiving commands (RCV), sending interrupts, and receiving interrupts.
3.MPI communication
MPI communication is a relatively simple communication method. The speed of MPI network communication ranges from 19.2Kbit/s to 12Mbit/s, supporting up to 32 nodes in the network. The maximum communication distance for MPI networks is 50 meters. For longer distances, communication can be extended using repeaters, although repeaters also occupy nodes.
MPI network nodes typically accommodate S7-200, human-machine interfaces, programming devices, intelligent ET200S, and RS485 repeaters, among other network components.
Siemens PLCs generally employ three communication methods for MPI communication between PLCs:
- Global Data Package Communication Method
- Connectionless Communication Method
- Connection-oriented Communication Method
4. Ethernet
The core concept of Ethernet is the utilization of a shared common transmission channel, a notion that originated from Xerox PARC in 1968. In 1972, Robert Metcalfe and David Boggs, both renowned networking experts, established a network connecting various ALTO computers along with an EARS laser printer.
This network marked the world's first personal computer local area network (LAN), which commenced its operation on May 22, 1973. On the inaugural day, Metcalfe drafted a memorandum proposing to rename the network as "Ethernet," drawing inspiration from the idea that "electromagnetic radiation could be transmitted through the ether by light." In 1979, DEC, Intel, and Xerox collectively standardized the network.
In 1984, thin coaxial Ethernet products emerged, followed by thick coaxial, twisted-pair, CATV coaxial, optical fiber, and various hybrid Ethernet products. Ethernet stands as one of the most popular topology standards worldwide, boasting numerous advantages such as high transmission rates, abundant network resources, robust system functionalities, straightforward installation, and ease of use and maintenance.
5.PROFIBUS-DP fieldbus
PROFIBUS-DP fieldbus is an open-field bus system that complies with both European and international standards.
The communication structure of PROFIBUS-DP is highly streamlined, offering high and stable transmission speeds, making it particularly suitable for communication between PLCs and distributed I/O devices in the field.