1  FUNCTION_BLOCK DIFFEQ

     2    VAR_INPUT

     3      RUN : BOOL ;             (* 1 = run, 0 = reset *)

     4      XIN : REAL ;

     5      A : ARRAY[1..] OF REAL ; (* Input coefficients *)

     6      M : INT ;                (* Length of input history  *)

     7      B : ARRAY[0..] OF REAL ; (* Output coefficients *)

     8      N : INT ;                (* Length of output history *)        

     9    END_VAR

    10    VAR_OUTPUT XOUT : REAL := 0.0 ; END_VAR

    11    VAR  (* NOTE : Manufacturer may specify other array sizes *)   

    12      XI : ARRAY [0..128] OF REAL ; (* Input history  *)

    13      XO : ARRAY [0..128] OF REAL ; (* Output history *)

    14      I : INT ;

    15    END_VAR

    16    XO[0] := XOUT ; XI[0] := XIN ;

    17    XOUT := B[0] * XIN ;

    18    IF RUN THEN

    19       FOR I := M TO 1 BY -1 DO

    20           XOUT := XOUT + A[I] * XO[I] ; XO[I] := XO[I-1];

    21       END_FOR;

    22       FOR I := N TO 1 BY -1 DO

    23           XOUT := XOUT + B[I] * XI[I] ; XI[I] := XI[I-1];

    24       END_FOR;

    25    ELSE

    26       FOR I := 1 TO M DO XO[I] := 0.0; END_FOR;

    27       FOR I := 1 TO N DO XI[I] := 0.0; END_FOR;

    28    END_IF ;

    29  END_FUNCTION_BLOCK

    30