(* 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 RAMP
   VAR_INPUT
     RUN : BOOL ;      (* 0 - track X0, 1 - ramp to/track X1 *)     
     X0,X1 : REAL ;
     TR : TIME ;       (* Ramp duration *)
     CYCLE : TIME ;    (* Sampling period *)
   END_VAR
   VAR_OUTPUT
     BUSY : BOOL ; (* BUSY = 1 during ramping period *)
     XOUT : REAL := 0.0 ;
   END_VAR
   VAR XI : REAL ;       (* Initial value *)
       T : TIME := T#0s; (* Elapsed time of ramp *)
   END_VAR
   BUSY := RUN ;
   IF RUN THEN
      IF T >= TR THEN BUSY := 0 ; XOUT := X1 ;
      ELSE XOUT := XI + (X1-XI) * TIME_TO_REAL(T)
                                / TIME_TO_REAL(TR) ;
           T := T + CYCLE ;
      END_IF ;
   ELSE XOUT := X0 ; XI := X0 ; T := t#0s ;
   END_IF ;
 END_FUNCTION_BLOCK