Mk20Clock: Complete correcting issues with CnV and add explanation.
Mk20Clock: Complete correcting issues with CnV and add explanation.

Also keep CnSC always configured in output-compare mode (cosmetical only).

ambrop72/aprinter,ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter,ambrop72/aprinter,johnkingsley/aprinter,johnkingsley/aprinter,ambrop72/aprinter,ambrop72/aprinter,ambrop72/aprinter,johnkingsley/aprinter,johnkingsley/aprinter,johnkingsley/aprinter