calling a serialport handle from a loop

[Robbo99]

Hi guys his my problem:
I am trying to run the function:

 Private Sub port_dataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles port.DataReceived

from inside a while loop of a different function ie.

 While A_switch = 0

            System.Threading.Thread.Sleep(100) ' Sleep for .1 second
            calabrate_send = calabrate_send - 5
            port.WriteLine("9 1 ")
            port.WriteLine(calabrate_send)
            port.WriteLine("a")
end While

the real problem is that the serial call updates the value of A_switch which is need to exit the loop at the correct time
if anyone knows how to do this or has a better method i would love to hear -cheers robbo