Thanks, John, for your detailed response. I am using Pronto emulation SW (TV Remote Controller 5 from pdawin.com) running on an iPAQ 3900 Pocket PC instead of a real Pronto. I learned the code form the OEM remote control. Following your advice, I generated a CCF file using MakeHex and HEx2CCF from NEC1.irp:
Device=32.64
Frequency=40000
and found that function 0 does indeed correspond to the ON/OFF function, as you surmised above.
Testing the remaining functions turned up most (if not all) of the original RC functions in the ranges 0-32 and 64-96 as you had supposed in your earler response to sekar.
Unfortunately, I found no discrete ON /OFF codes. I was also hoping to find discrete codes for the different screen formats, which can also be controlled directly via RS-232, but no luck here either. All I succeeeded in doing was to reset the TVs channel assignment programming, which will cost me quite a bit of time to reconstruct.
Thanks anyway for your very competent and prompt assistance!