Hi,
the game you are playing is related to the defined sizes of bitfield elements (unsigned char, unsigned int) and then MSB. LSB order, MSb, LSb order. I suggest you to test combinations simply with different options after reading the help ....

If you want more info about bitfields I suggest to go through all appearnces in

Plus when you select an item it can show more options with the same name. Open each of them because each of them direct to different contet.

... or go to your instalation dir c:\Program Files (x86)\Freescale\CWS12v5.2\Help\pdf\
open file Compiler_HC12.pdf
and search for each existence of bitfield keyword.
Best regards,
Ladislav