Function block instances are stored as one block in memory. This is necessary so that the same code can work on different instances. If a variable is marked with ‎RETAIN‎ in a function block, then each instance of the function block is protected with all variables. This is also true for the variables of the function block that are not marked this way. 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.