PLC Programming

Defined data types
References
For example, if you have a structure named "Week" that contains a component named "Monday", you
can get to it by doing the following:
Week.Monday
You can use the user-defined reference data type to create an alternative name for a variable,
constant or function block.
Create your references as objects in the Object Organizer under the register card
They begin with the keyword TYPE and end with END_TYPE.
Syntax:
TYPE : ;
END_TYPE
Example:
TYPE message:STRING[50];
END_TYPE;
Data types.
Subrange types
A subrange type is a type whose range of values is only a subset of that of the basic type. The
declaration can be carried out in the data types register, but a variable can also be directly declared
with a subrange type:
Syntax for the declaration in the 'Data types' register:
TYPE : (..) END_TYPE;
must be a valid IEC identifier,
is one of the data types SINT, USINT, INT, UINT, DINT, UDINT, BYTE, WORD,
DWORD (LINT, ULINT, LWORD).
Is a constant which must be compatible with the basic type and which sets the
lower boundary of the range types. The lower boundary itself is included in this
range.
Is a constant that must be compatible with the basic type, and sets the upper
boundary of the range types. The upper boundary itself is included in this basic
type.
Examples:
TYPE
SubInt : INT (-4095..4095);
END_TYPE
Direct declaration of a variable with a subrange type:
VAR
i : INT (-4095..4095);
ui : UINT (0..10000);
END_VAR
If a constant is assigned to a subrange type (in the declaration or in the implementation) that does not
fall into this range (e.g. 1:=5000), an error message is issued.
In order to check for observance of range boundaries at runtime, the functions CheckRangeSigned
or CheckRangeUnsigned must be introduced. In these, boundary violations can be captured by the
appropriate method and means (e.g. the value can be cut out or an error flag can be set.). They are
implicitly called as soon as a variable is written as belonging to a subrange type constructed from
either a signed or an unsigned type.
10-36 CoDeSys V2.3