Glossary¶
BOOL
Variables of the type BOOL can have the values TRUE and FALSE. For this, 8 bit of memory space are reserved.
BYTE
BYTE belongs to the integer data types. The different numerical types are responsible for a different numerical range.
| TYPE | BYTE |
|---|---|
| Lower limit | 0 |
| Upper limit | 255 |
| Memory space | 8 bits |
Due to this, it is possible that information are lost when converting greater data types to smaller data types.
DINT
DINT belongs to the integer data types. The different numerical types are responsible for a different numerical range.
| TYPE | DINT |
|---|---|
| Lower limit | -2147483648 |
| Upper limit | 2147483647 |
| Memory space | 32 bits |
Due to this, it is possible that information are lost when converting greater data types to smaller data types.
DWORD
DWORD belongs to the integer data types. The different numerical types are responsible for a different numerical range.
| TYPE | DWORD |
|---|---|
| Lower limit | 0 |
| Upper limit | 4294967295 |
| Memory space | 32 bits |
Due to this, it is possible that information are lost when converting greater data types to smaller data types.
INT
INT belongs to the integer data types. The different numerical types are responsible for a different numerical range.
| TYPE | INT |
|---|---|
| Lower limit | -32768 |
| Upper limit | 32767 |
| Memory space | 16 bits |
Due to this, it is possible that information are lost when converting greater data types to smaller data types.
WORD
WORD belongs to the integer data types. The different numerical types are responsible for a different numerical range.
| TYPE | WORD |
|---|---|
| Lower limit | 0 |
| Upper limit | 65535 |
| Memory space | 16 bits |
Due to this, it is possible that information are lost when converting greater data types to smaller data types.
Functions
Functions are subroutines which have multiple input parameters and return exactly one result element. The returned result can be of an elementary or a derived data type. Due to this, a function may also return an array, a structure, an array of structures and so on. For the same input parameters, functions always return the same result (they do not have an internal memory).
Therefore, the following rules can be derived:
- Within functions, global variables can neither be read nor written.
- Within functions, absolute operands can neither be read nor written.
- Within functions, function Function Blocks must not be called.
Function Blocks
Function Blocks are subroutines which can have as many inputs, outputs and internal variables as required. They are called from a program or from another Function Block. As they can be used several times (with different data records), Function Blocks (code and interface) can be considered as type. When assigning an individual data record (declaration) to the Function Block, a Function Block instance is generated. In contrast to functions, Function Blocks can contain statically local data which are saved from one call to the next. Therefore e.g. counters can be realized which may not forget their counter value. I.e. Function Blocks can have an internal memory.
Functions and Function Blocks differ in two essential points:
- A Function Block has multiple output parameters, a function only one. The output parameters of functions and Function Blocks differ syntactically.
- In contrast to a function, a Function Block can have an internal memory.
Function Blocks with historical values (memory)
For Function Blocks with historical values it has to be observed that instance names may not be defined several times if different data sets should be called.
Function Blocks without historical values (memory)
For Function Blocks without historical values only one instance has to be defined for the Function Block type. This instance can be used for several calls of the Function Block (also with different I/O values).