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

     2 

     3 (*

     4  * An IEC 61131-3 IL and ST compiler.

     5  *

     6  * Based on the

     7  * FINAL DRAFT - IEC 61131-3, 2nd Ed. (2001-12-10)

     8  *

     9  *)

    10 

    11 

    12 (*

    13  * This is part of the library conatining the functions

    14  * and function blocks defined in the standard.

    15  *

    16  * Counter function blocks

    17  * -----------------------

    18  *)

    19 

    20 

    21 FUNCTION_BLOCK CTU

    22   VAR_INPUT

    23     CU : BOOL;

    24     R : BOOL;

    25     PV : INT;

    26   END_VAR

    27   VAR_OUTPUT

    28     Q : BOOL;

    29     CV : INT;

    30   END_VAR

    31   VAR RETAIN

    32     PVmax : INT;

    33   END_VAR

    34   IF R THEN CV := 0 ;

    35   ELSIF CU AND (CV < PVmax)

    36        THEN CV := CV+1;

    37   END_IF ;

    38   Q := (CV >= PV) ;

    39 END_FUNCTION_BLOCK

    40 

    41 

    42 FUNCTION_BLOCK CTD

    43   VAR_INPUT

    44     CD : BOOL;

    45     LD : BOOL;

    46     PV : INT;

    47   END_VAR

    48   VAR_OUTPUT

    49     Q : BOOL;

    50     CV : INT;

    51   END_VAR

    52   VAR RETAIN

    53     PVmin : INT;

    54   END_VAR

    55   IF LD THEN CV := PV ;

    56   ELSIF CD AND (CV > PVmin)

    57       THEN CV := CV-1;

    58   END_IF ;

    59   Q := (CV <= 0) ;

    60 END_FUNCTION_BLOCK

    61 

    62 

    63 FUNCTION_BLOCK CTUD

    64   VAR_INPUT

    65     CU : BOOL;

    66     CD : BOOL;

    67     R  : BOOL;

    68     LD : BOOL;

    69     PV : INT;

    70   END_VAR

    71   VAR_OUTPUT

    72     QU : BOOL;

    73     QD : BOOL;

    74     CV : INT;

    75   END_VAR

    76   VAR RETAIN

    77     PVmax : INT;

    78     PVmin : INT;

    79   END_VAR

    80   IF R THEN CV := 0 ;

    81   ELSIF LD THEN CV := PV ;

    82   ELSE

    83     IF NOT (CU AND CD) THEN

    84       IF CU AND (CV < PVmax)

    85       THEN CV := CV+1;

    86       ELSIF CD AND (CV > PVmin)

    87       THEN CV := CV-1;

    88       END_IF;

    89     END_IF;

    90   END_IF ;

    91   QU := (CV >= PV) ;

    92   QD := (CV <= 0) ;

    93 END_FUNCTION_BLOCK

    94