Provided by standard library.
Resetting bistable function blocks
Q1 = RS (SET, RESET1) means:
Q1 = NOT RESET1 AND (Q1 OR SET)
The input variables SET and RESET1 as well as the output variable Q1 are type BOOL.
Declaration example
RSInst : RS ;
Example in Function Block Digram

Example in Structured Text
RSInst(SET:= VarBOOL1 , RESET1:=VarBOOL2 );
VarBOOL3 := RSInst.Q1 ;