The data type ‎BIT‎ is valid only in structures for the declaration of structure members or in a function block for the declaration of variables. A ‎BIT‎ variable can have the values ‎TRUE‎ (1) and ‎FALSE‎ (0). In this case, the variable requires exactly one bit of memory.

As a result, you can symbolically address individual bits by a name. ‎BIT‎ variables that are declared in succession are bundled in bytes. In this way, you can optimize memory use as opposed to ‎BOOL‎ types, which reserve 8 bits each. On the other hand, bit access is significantly more time-consuming. Therefore, you should use the ‎BIT‎ data type only when you need to define data in a predefined format.