> i have to implement X.25 packet radio protocol on PIC16C77.
>
> Any ideas or code would be much appreciated.

I do it by sending serial (ascii) data to a terminal node controller
(TNC).  The TNC does all the work.  The smallest package for doing
this that I know of is the MIM module by Clement Engineering.  You
can find them by doing a web search on Agrelo Engineering who sells
the radio transmitter you can interface to it.

Lloyd