A fileevent question

Hello out there,
just asking for inspiration.
I have a simulation which executes commands - everything ok.
But now the program should also communicate with external hardware via
a serial connection and that is the problem:
- I don't want to block waiting for an answer since I also have a GUI.
- Turning to file events I now have the problem that the simulation
cannot continue before a particular call to the hardware is complete:
It may ask the hardware for a particular value which is to be used in
the next command.

So my question is: How do I block execution of the simulation part
until an answer arrives /without/ blocking the whole app?
- An attempt to use 'vwait' resulted in the whole app freezing.
- A separate thread would probably solve this problem.
- A coroutine would instinctively be a "lighter" solution but I have
so far never used coroutines and didn't find an example which seemed
to "fit" my situation.
- Any other way ...

Any idea, tip or link will be greatly appreciated
Helmut

Sorry,
wrong news group.
Helmut