Hello Seyoung,
please see below an answer from an application engineer.
DESCRIPTION
The CAN or UART connection is describing just physical layer which is transferring data to FreeMASTER based GUI. The functionality of this demo is the same with both interfaces. Please don’t expect other functions became available when CAN is used.
Only some of the USB-CAN converter are supported by FreeMASTER. The list of supported devices are available in FreeMATER. Other devices are not supported. Board was tested with Vector and Kvaser converters.
To change form UART to CAN you should apply only following settings:

So maybe switching to FMSTR_POLL_DRIVEN mode will solve your problem.
With Best Regards,
Jozef