Hi,
If first 5 bytes received are correct then GOTO start.
No.... It checks the first 5 bytes, if any of them is NOT "A" it jumps to start.

In this case if first 5 bytes received correctly and last 5 bytes are wrong? It runs "start" subroutine without checking the last 5 bytes?
No.... If it finds that the first 5 bytes are received correct it continues to check the last 5 bytes. If they TOO are correct it extracts the data. If any of the last the 5 bytes are wrong it'll jump back to start without extracting the data.

Only when the first bytes are "A" AND the last 5 bytes are "E" will it extract the data. As soon as ANY of the first 5 bytes OR the last 5 bytes does NOT match will it jump back to start - which is whay you said it should do:
if all conditions matched (receive first 5 "A" and last 5 "E" properly) then store data_in
/Henrik.