S7- The 200 series PLC free communication port initialization and Siemens PLC communication instruction

Under the communication mode, communication port is completely controlled by the user program, communication protocol is set by the user. Is a master-slave relationship between PC and PLC, PC has always been in a dominant position. PLC communication programming is first to a serial port initialization, S7 - 200 PLC controller initialization is based on the special mark SMB30 ( Port 0) SMB130 ( Port 1) Written communication control, set the baud rate of communication, parity, stop bits and characters in length. Clearly, the set must be consistent with the PC Settings. SMB30 and SMB130 you and meaning is as follows: among them, the calibration method: 00 and 11 are no calibration, 01 for parity, 10 surprising; Length: 0 for transmitting valid data is eight characters, 1 is the valid data is seven; Baud rate: 000 is 38400 baud, 001 is 19200 baud, 010 to 9600 baud, 011 is 4800 baud, 100 is 2400 baud, 101 to 1200 baud, 110 is 600 baud, 111 is 300 baud; Communication protocol: 00 for PPI protocol for freedom from station mode, 01 mouth, 10 for PPI protocol host mode, 11 to retain the default Settings for PPI protocol from standing model. XMT and RCV orders for PLC controller to send and receive data to the outside world. When PLC RUN conditions, communication command is valid, when the PLC controller is in a state of STOP communication command is invalid. XMT command to specify storage area of data are transmitted through the specified PORT, when the last byte memory area is transferred, the PLC will generate an interrupt, command format for XMT TABLE, the PORT, which used to send communication PORT, the PORT specified PLC TABLE as data store address, the first byte to store the number of bytes to be transmitted, namely the data length, the maximum is 255. RCV command from the specified PORT to read data stored in the specified data storage area, when the last byte receive end, the PLC will generate an interrupt, command format for RCV TABLE, PO RT, PLC through the PORT PORT receives the data, and the data stored in the TBL data storage area, the TABLE of the first byte is received bytes. In the free port communication mode, but also can receive data through characters interrupt control, the PLC will each receive a byte of data to produce an interrupt. Thus, the PLC each receive a byte of data can be in the corresponding interrupt program to deal with the received data.
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