Several methods of serial communication of Siemens PLC

Most third-party devices support it, and Siemens S7PLC can control serial communication by choosing free port communication mode. In the simplest case, only the send command (XMT) is used to send information to third-party devices (such as printers or frequency converters). In any case, it must be realized by S7 PLC programming. When the free port mode is selected, the user can control the operation of the communication port by sending instructions (XMT), receiving fingers (RCV), sending interrupts and receiving interrupts. 2.PPI communication PPI protocol is the most basic communication mode of S7-200CPU, and communication can be realized through its own port (PORT0 or PORT 1), which is the default communication mode of S7-200 CPU. PPI is a master-slave protocol communication, and the master-slave station is in the token ring network. Users can read and write instructions on the network in the CPU, which means that the network reading and writing instructions run on PPI protocol. So PPI can only write programs at the master station, and it is meaningless to read and write instructions from the slave station's network. 3.MPI communication MPI communication is a relatively simple communication method. The communication rate of MPI network is19.2kbit/s ~12mbit/s, MPI network can support the connection of 32 nodes at most, and the maximum communication distance is 50M. The communication distance is long, and the communication distance can be extended through the repeater, but the repeater also takes up nodes. MPI network nodes can generally hang S7-200, man-machine interface, programming equipment and so on.