Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Fujitsu/MB9BF41xS/BTIOSEL03/BTSEL0123#0x0
I/O Select Register
I/O select bits for Ch.0/Ch.1
I/O select bits for Ch.2/Ch.3
https://github.com/cmsis-svd/cmsis-svd-data