Thanks guys,

OK, I already figured some external memory might be necessary to fit the code into prior to the actual reprogramming of remote Pic.

The GPRS modem will have a TCP/IP stack so the file will be FTPed across air. So, that will deal with the data integrity of the firmware that reaches the actual hardwired network.

When sending to the ultimate destination transmitting it twice and doing a compare sounds a good idea. It might end up more than twice but as long as it doesn't loose integrity that will be fine.

Using a bootloader should eliminate the problem of failed firmware upgrade requiring a trip to 'shop' as the code will not be loaded unless it has been received error free providing the bootloader has the smarts.

I guess what I need is bootloader code for a Pic. I am not clever enough (yet!) to write it so has anyone got any starting points for me? I bet someone has written one even if not in the PBP world. Hummm, a wider google search needed I think. I will post anything I find as this thread could be interesting as it develops.

Thanks

Rich