That is the code for your reader. What is the sender? Is it another LabVIEW program? Another device or instrument? You are only giving us half the story.
And old way of controlling serial communication that is rarely used any more is that if your serial cable is wired for it, you can use hardware control lines, aka hardware handshaking for the two systems to signal to each other when they are ready to receive data. There is also a setting for software control.
But it is impossible to recommend anything without know what is happening on the other end.
