You can loop the Serin2 or the Serin until the predetermined "Flag" is found.

Loop:
serin datapin....variable.
Process by storing data in Eprom or whatever
if variable <> CR (or flag) goto Loop:

This is assuming you are reading 1 char at a time.

I don't know how your data is being sent... but you can read a string of char and check for the "Flag" before looping back.

Dwayne