bah as you wish. You can even do some handshake between PIC and PC.

PIC side:
  1. Waiting for Flag (must be Fix format 1,2,3 or more character) Lets'say BEER
  2. choose according procedure to do (Corect HSERIN), Send Confirmation to PC (OK i got Beer, send me another Crate now)

and there still many other way.. it's up to you