Coils can also be defined as set or reset coils. One can recognize a set coil by the "S" in the coil symbol: (S)) It never writes over the value TRUE in the appropriate Boolean variable. That is, if the variable was once set at TRUE, then it remains so.

One can recognize a reset coil by the "R" in the coil symbol: (R)) It never writes over the value FALSE in the appropriate Boolean variable: If the variable has been once set on FALSE, then it remains so.