Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Fujitsu/MB9BF41xS/BTIOSELCF/BTSELCDEF#0x0
I/O Select Register
I/O select bits for Ch.C/Ch.D
I/O select bits for Ch.E/Ch.F
https://github.com/cmsis-svd/cmsis-svd-data