A function block instance is always stored completely in memory. This is necessary so that the same code can work on different instances. If only one variable in a function block is marked with ‎PERSISTENT‎, then the function block instance is stored completely with all variables in remanent memory, although only the one variable is treated as persistent. However, non-volatile memory is not available to the same extent as main memory.

A function block with a pointer to an instance in SRAM as a variable is not stored in the protected memory.