There are two types of flip-flops in Siemens S7-300 and S7-400 PLCs. SR and RS.
In the SR flip-flop, if the "S" input is turned on, even momentarily,
Output "Q" is permanently on.
If the "R" input turns on, the "Q" output turns off.
in tthe SR Flip Flop , If the "S" and "R" inputs are turned on together,
Output "Q" turns off.
in tthe RS Flip Flop , If the "S" and "R" inputs are turned on together,
Output "Q" turns on.

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