Definition of sm.0 in Siemens plc programming

SM0.0, the PLC is always 1 when it is running, it is a constant ON relay.

SM0.1, the first scan of the PLC is 1, one scan cycle. Generally used to initialize the program.

SM0.2, if the data is lost, change to 1, one scan cycle.

SM0.3, enter RUN mode, close one scan cycle

SM0.4, clock with a period of 1 minute and a duty cycle of 0.5, ON 30S OFF 30S

SM0.5, clock with a period of 1 second and a duty cycle of 0.5

SM0.6, scan clock pulse, this scan is set to 1, the next scan is set to 0, and it is executed continuously. Can be used as a scan counter.

SM0.7, indicates the position of the CPU working mode switch, and 0 is the Term position. 1 is the Run position.