Hello Shumpi55,
Yes, in order to use the built-in level shifter, you need to place jumper J8 in COM_EN position, configure PTC5 as an output and force it to 1:
PTCDD_PTCDD5 = 1; // PTC5 as an output
PTCD_PTCD5 = 1; // PTC5 = high
This sequence is not present on example 11.10 in my book (because I tested it using the built-in BDM serial channel). I'll update the errata file with a tip about that and add the proper code sequence.
Best regards,