Siemens PLC serial communication method

1, RS485 serial communication
Most third-party device support , Siemens S7 PLC by selecting the free port communication mode control serial communication. In the simplest case only send information to the third party equipment , such as printers or the transmission frequency instruction (XMT). In either case , must be achieved through the S7 PLC programming. When you select a free port mode , the user can send commands (XMT), the receiving means (RCV), transmit interrupt , receive interrupt to control the communication port operations.
2, PPI communication
S7-200CPU PPI protocol is the most basic means of communication , through their original port (PORT0 or PORT1) can achieve communication , S7-200 CPU is the default method of communication . PPI is a master – slave protocol communication, the master – from standing in a token ring network. User network within the CPU can read and write commands , meaning that the network read and write commands are run on the PPI protocol. Thus PPI writing program only on the master side can be, read and write commands from the network station does not make sense .
3, MPI communication
MPI communication is a simple means of communication,MPI network ommunication speed is 19.2Kbit / s ~ 12Mbit / s, MPI network supports up to 32 nodes , the maximum communication distance of 50M. Communication distance, you can also extend the communication distance via repeaters, but also consumes repeater nodes.MPI network nodes can usually hang S7-200, HMI , programming equipment.

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