(* Following taken directly from the IEC 61131.3 draft standard *)

(*
 * An IEC 61131-3 IL and ST compiler.
 *
 * Based on the
 * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)
 *
 *)

 FUNCTION_BLOCK INTEGRAL
   VAR_INPUT
     RUN : BOOL ;       (* 1 = integrate, 0 = hold *)
     R1 : BOOL ;        (* Overriding reset        *)
     XIN : REAL ;       (* Input variable          *)
     X0  : REAL ;       (* Initial value           *)
     CYCLE : TIME ;     (* Sampling period         *)
   END_VAR
   VAR_OUTPUT
     Q : BOOL ;         (* NOT R1                  *)
     XOUT : REAL ;      (* Integrated output       *)
   END_VAR
   Q := NOT R1 ;
   IF R1 THEN XOUT := X0 ;
   ELSIF RUN THEN XOUT := XOUT + XIN * TIME_TO_REAL(CYCLE);
   END_IF ;
 END_FUNCTION_BLOCK