Tom,
AFAIK there's no such tool and never will. Serial Comm on a computer is per se asynchronous. Incoming data are received in a kind of UART chip and stored in its buffer. When a given filling level of the buffer (or a given delay) is reached, an interrupt is raised and the data is transformed to the application level program (your exe). The same holds true when sending data.
This is always decoupled and as such asynchronous. One would need a dedicated CPU (µC) to fully reach synchronous transactions.
There is a property to perform serial transactions synchronously. This would, however, just prevent LabVIEW from doing any other things before the required transaction is finished. On the system and driver level there is just marginal change, AFAIK.
I would not believe that the synchronous transaction you mentioned is really required or is what I understood from your Q.
HTH and Greetings from Germany!
--
Uwe
