Use duplicate symtable instead of symtable for enum constant value table (this will later allow us to detect semantic errors in IEC 61131-3 source code)
FUNCTION_BLOCK LAG1
VAR_INPUT
RUN : BOOL ; (* 1 = run, 0 = reset *)
XIN : REAL ; (* Input variable *)
TAU : TIME ; (* Filter time constant *)
CYCLE : TIME ; (* Sampling time interval *)
END_VAR
VAR_OUTPUT XOUT : REAL ; END_VAR (* Filtered output *)
VAR K : REAL ; (* Smoothing constant, 0.0<=K<1.0 *)
END_VAR
IF RUN THEN XOUT := XOUT + K * (XIN - XOUT) ;
ELSE XOUT := XIN ;
K := TIME_TO_REAL(CYCLE) / TIME_TO_REAL(CYCLE + TAU) ;
END_IF ;
END_FUNCTION_BLOCK