Variables of the data type BOOL are binary variables. They can only have the value 0 or 1, and always have a width of 1 bit.
The condition 0 corresponds to FALSE (e.g. initial value in the POU header) and means that the variable is switched off. In this case we also speak of the variable not being set.
The condition 1 corresponds to TRUE (e.g. initial value in the POU header) and means that the variable is switched on. In this case we also speak of the variable being set.
The default initial value, e.g. for the variable declaration in the POU header or in the global variable list = 0 (FALSE). In this case the variable is not set during the PLC program start. If this is not the case, the initial value may also be set to TRUE.