One, PPI communication
PPI protocol is the most basic communication method of S7-200 CPU, through the original own port (PORT0 or PORT1) can realize the communication, is the default communication method of S7-200 CPU.
PPI is a master-slave protocol communication, master-slave station in a token ring network. It is sufficient to read and write commands to the user network within the CPU, which means that the network read and write commands are running on the PPI protocol. Therefore, PPI can be programmed only on the master side, and the network read and write commands from the slave are meaningless.
Two, RS485 serial communication
Most of the third-party devices support, Siemens S7 PLC can control the serial communication by selecting the free port communication mode. The simplest case is to send information to third-party devices such as printers or inverters using only the Send command (XMT). In either case, this must be achieved by writing a program through the S7 PLC.?
When the free port mode is selected, the user can control the operation of the communication port by using the send command (XMT), receive command (RCV), send interrupt, and receive interrupt.
Three, MPI communication
MPI communication is a relatively simple way of communication, MPI network communication rate is 19.2Kbit/s ~ 12Mbit/s, MPI network supports up to 32 nodes connected to the maximum communication distance of 50M. the communication distance is far away, you can also extend the communication distance through the repeater, but the repeater also occupies nodes.
MPI network nodes can usually hang S7-200, human-machine interface, programming equipment, intelligent ET200S and RS485 repeaters and other network components.
The MPI communication between Siemens PLC and PLC generally has three kinds of communication mode:
1, global packet communication mode
2, no configuration connection communication mode
3, configuration connection communication mode?
Four, Ethernet communication
The core idea of Ethernet is the use of *** enjoy the public **** transmission channel. In 1972, Metcalfe and David Boggs (both famous network experts) set up a set of networks, which connects different ALTO computers together, as well as EARS laser printers.
Metcalfe wrote a memo on the day of the first run, which was to rename the network Ethernet, inspired by the idea that electromagnetic radiation could be propagated by a glowing Ether. In 1979, DEC, Intel and Xerox*** worked together to standardize the network.
V. PROFIBUS-DP communication
In 1984, thin-cable Ethernet products appeared, and later appeared thick cable, twisted-pair, CATV coaxial cable, fiber optic cable, and a variety of media mixed Ethernet products. Ethernet is currently one of the world's most popular topology standards, with high transmission and dissemination rates, rich network resources, strong system functions, simple installation and easy to use and maintain many advantages.
PROFIBUS-DP fieldbus is an open fieldbus system that complies with European and international standards.PROFIBUS-DP communication has a very streamlined structure, high and stable transmission speeds, and is ideally suited for communication between PLCs and decentralized I/O devices in the field.
Expanded Information
The programming languages used in PLCs are ladder diagrams, Boolean mnemonics, function charts, function blocks and statement description programming languages. The diversity of programming methods makes programming simple and the application surface expansion. Operation is very flexible and convenient, monitoring and controlling variables is very easy.
Siemens PLC S7-300 series PLC installation and notes:
1, the auxiliary power supply power is small, can only drive small power devices (photoelectric sensors, etc.).
2, general PLC have a certain number of possession points (i.e., empty address terminals), do not connect the line.
3, PLC there is a delay in the I / O response, especially in the fast response equipment should be noted.
4, output relay type, transistor type (high-speed output is recommended), the output can be directly with light loads (LED indicators, etc.).
5, input/disconnect time should be greater than the PLC scan time.
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