The device memory data cannot be stored in a memory cassette.
In the FX3U/FX3UC series, a part of device memory data can be latched using a battery.
The device memory data can be written to or read from the built-in RAM of a programmable controller and stored as part of the project data using a programming tool such as GX Works2.

For details, refer to the following.
　Section 15.1 in the GX Works2 Version 1 Operating Manual (Common) (Manual number: SH-080779ENG)
　　
Data, such as programs, parameters, comments, file register, symbolic information, and extended file register, can be stored in a memory cassette.

* For details on the latch range setting, refer to the following.
Section 2.7 in the FX3S/FX3G/FX3GC/FX3U/FX3UC Series Programmable Controllers Programming Manual [Basic & Applied Instruction Edition] (Manual number: JY997D16601)

Reference) The main units with Ver. 3.00 or later support symbolic information.
　　　Since the capacity of symbolic information is large, use of the FX3U-FLROM-1M which has the dedicated areas for storing symbolic information is recommended.