Using function blocks for implicit checks

TwinCAT provides special POUs, which implement implicit monitoring functions. You can add these special POUs to an application to make implicitly provided monitoring functionality available. At runtime these functions check the bounds of arrays or subrange types, the validity of pointer addresses, or division by 0. Note that this capability may be disabled on devices if such test function blocks are provided by a specific implicit library.

Additional information
Object POUs for implicit checks