Private Sub Button1_Click(ByVal sender As Object, ByVal _e As EventArgs) Handles Button1.Click
If Button1.Text = "Close" Then ' will fail it button's text is " Close" (notice the extra space)
SerialPort1.Close()
Button1.Text = "Open"
Else
If Not SerialPort1.IsOpen Then SerialPort1.Open() ' where is endif ?
Button1.Text = " Close" ' one extra space!
End If
End Sub
Where do you set the port options (baud rate, etc. ?).