1756-BA1 Before system operation, the PLC communication parameters should be set, including baud rate, parity mode, number of data bits and number of stop bits, etc. This setting should be consistent with the host computer. When using the free port mode in S7-226 for serial communication with the host computer, it can be set by special register SMB30 (port 0) or SMB130 (port 1). The following is an example of the generator no-load shutdown experiment to illustrate the operation of the system.

When the 1756-BA1 machine stops under normal no-load, the PLC detects the stop signal, sets the fault flag, and then records the data 13 seconds after the stop. Run the host computer programme, in the main interface, press the “transfer” button, the host computer began to read the data in the PLC. Wait until the programme prompts “data transfer is complete”, press the “display” button, the “waveform display” window will pop up as shown in Figure 3. As can be seen from the figure, the curve reflects the changes of machine voltage and excitation current before and after the generator shutdown.