You can configure a function block with a memory reserve to prevent its function block instances from having to be copied to new memory locations during an online change. This can happen when you make declaration changes for example adding variables to the function block. With memory reserves, this kind of online change runs faster and fewer problems occur. When the memory reserve is depleted, a message is displayed before the online change is performed.

NOTICE

The memory reserve for a function block is best configured before downloading the application to the controller for the first time. If the memory reserve is configured when the application exists on the controller, then a more complicated online change is necessary.