Not really since you only do that once before the loop so anything after that is valid. You only do that more than once if getting out of the loop and do the same or a different write/read operation but usually a few bytes do not affect much. The serial port works best if you have some handshaking scheme like looking for a distinct checksum for each write or read.
The flush buffer icon is under diagram function pallete/instruments IO/serials/. Just add this VISA flush pallete to the Dennis approach should also work too.
Thanks alot for napview and Dennis for you help, I attach an VI program that writes the ASCII character "A" waits till an ASCII character "B" from the serial port , Thanks alot for your help guys
It looks ok but the write should be inside the loop: logic is keep writing until a B is read and get out of the loop to do something else. Also there is no need to flush it after the write because this could get rid of that important B character from the device. Your logic might be the A character is still in the buffer but that would not affect anything coming from the device. But does this vi always work? If not try what has been suggested.
