From which to which number is the range of latch device（Power failure retention area）? Can the link register (W) and file register (R) be latched?

The latch range can be set arbitrarily by the customer.
The settings can be found in the memory/device settings of CPU parameters.
To back up the link register (W) and file register (R) devices, a battery FX3U-32BL (option) is required.