Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Fujitsu/MB9BF41xS/BTIOSEL8B/BTSEL89AB#0x0
I/O Select Register
I/O select bits for Ch.8/Ch.9
I/O select bits for Ch.A/Ch.B
https://github.com/cmsis-svd/cmsis-svd-data