PLC Programming

Defined data types
FUNCTION CheckBounds : INT
VAR_INPUT
index, lower, upper: INT;
END_VAR
IF index < lower THEN
CheckBounds := lower;
ELSIF index > upper THEN
CheckBounds := upper;
ELSE CheckBounds := index;
END_IF
The following sample program for testing the CheckBounds function exceeds the bounds of a defined
array. The CheckBounds function allows the value TRUE to be assigned, not to location A[10], but to
the still valid range boundary A[7] above it. With the CheckBounds function, references outside of
array boundaries can thus be corrected.
Test Program for the function CheckBounds:
PROGRAM PLC_PRG
VAR
a: ARRAY[0..7] OF BOOL;
b: INT:=10;
END_VAR
a[b]:=TRUE;
Pointer
Enumeration
Variable or function block addresses are saved in pointers while a program is running.
Pointer declarations have the following syntax:
: POINTER TO ;
A pointer can point to any data type or function block even to user-defined types.
The function of the Address Operator ADR is to assign the address of a variable or function block to
the pointer.
A pointer can be dereferenced by adding the content operator "^" after the pointer identifier.
Example:
pt:POINTER TO INT;
var_int1:INT := 5;
var_int2:INT;
pt := ADR(var_int1);
var_int2:= pt^; (* var_int2 is now 5 *)
Enumeration is a user-defined data type that is made up of a number of string constants. These
constants are referred to as enumeration values.
Enumeration values are recognized in all areas of the project even if they were declared within a
POU. It is best to create your enumerations as objects in the Object Organizer under the register card
Syntax:
Data types. They begin with the keyword TYPE and end with END_TYPE.
TYPE :( ,, ...,);
END_TYPE
A variable of the type can take on one of the enumeration values and will be initialized
with the first one. These values are compatible with whole numbers which means that you can
perform operations with them just as you would with INT. You can assign a number x to the variable. If
the enumeration values are not initialized, counting will begin with 0. When initializing, make certain
the initial values are increasing. The validity of the number will be reviewed at the time it is run.
Example:
TYPE TRAFFIC_SIGNAL: (Red, Yellow, Green:=10); (*The initial value for each of the colors is
red 0, yellow 1, green 10 *)
10-34 CoDeSys V2.3