Public Class Form1
    Dim time As Integer = 0
    Dim run As Boolean = False
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        SerialPort1.PortName = "COM2"
        SerialPort1.RtsEnable = True
        SerialPort1.DtrEnable = True
    End Sub
 
    Public Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Timer1.Tick
        time = time + 1
        TextBox1.Text = time
    End Sub
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        SerialPort1.Open()
    End Sub
    Private Sub SerialPort1_PinChanged(ByVal sender As Object, ByVal e As _
      System.IO.Ports.SerialPinChangedEventArgs) Handles SerialPort1.PinChanged
        If SerialPort1.CtsHolding Then
            MsgBox("high")
        Else
            Timer1.Start()
            MsgBox("low")
        End If
End Sub

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