:)Dear Elliot,
Thank you for your help. I have just found the solution:-
Activate KEYBOARD in the CS2 menu,
Activate CONFIGURE KEYBOARD,
Activate the ICON Blue Arrow pointing south,
then activate the program button on the 5235 decoder,
lastly, activate the three-way decoder icon on the CS2 KEYBOARD display - bingo - it works.
Best Regards Dave CONNER.