I agree with Erik,

using a watchdog to handle wrong data input was really a very poor solution.

Serial data input must be handled than any other user interface. E.g. like the user can turn any knob and press any key without causing malfunction or damage.

E.g. transmit a CRC at the end to check if data was corrupted. Also add consistence check on every data package, e.g. right number of bytes, values always in range, valid commands received and so on.

Peter