USB converted serial I/O behaves differently from pure HW serial I/O in
timing wise; that's, how bit pattern is generated, transfered and
recognized to reproduce character stream illusion. USB serial involves
larger and variable delay amount compared to real HW serial operation,
I guess. It might end up with "protocol error" for a particular implementation
of serial application. That's just my impression without hand-on proof by
measuring high precision instruments.
Toru Nishimura / ALKYL Technology