calling a serialport handle from a loop

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

Code:

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

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from inside a while loop of a different function ie.

Code:

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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

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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

Show more code.

solved the problem using

Code:

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System.Windows.Forms.Application.DoEvents()

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however this results in a heep of data at the serialport buffer built up hence i might need to use clear to send i guess
thanks