serial port VB.net ทำไมถึงไม่มีการ return ค่ากลับมาครับ

Imports System.Data
Imports System.Data.SqlClient
Imports VB = Microsoft.VisualBasic
Imports System.IO.Ports
Imports System.Threading
Imports System.ComponentModel
Imports System
Public Class Form1

    Dim myPort As Array
    Delegate Sub SetTextCallback(ByVal [text] As String) 'Added to prevent threading errors during receiveing of data

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        TextBox1.Text = ""
        txtSN.Enabled = False
        btSend.Enabled = False

        myPort = IO.Ports.SerialPort.GetPortNames()
        cmbBaud.Items.Add(9600)
        cmbBaud.Items.Add(19200)
        cmbBaud.Items.Add(38400)
        cmbBaud.Items.Add(57600)
        cmbBaud.Items.Add(115200)
        For i = 0 To UBound(myPort)
            cmbPort.Items.Add(myPort(i))
        Next
        cmbPort.Text = cmbPort.Items.Item(0) 'Set cmbPort text to the first COM port detected
        cmbBaud.Text = cmbBaud.Items.Item(4) 'Set cmbBaud text to the first Baud rate on the list

        

    End Sub

    
    Private Sub btnConnect_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConnect.Click

        If SerialPort1.IsOpen = True Then
            SerialPort1.Close()
            btnConnect.Text = "connect"
            
            txtSN.Enabled = False
            btSend.Enabled = False
        Else
            SerialPort1.PortName = cmbPort.Text 'Set SerialPort1 to the selected COM port at startup
            SerialPort1.BaudRate = cmbBaud.Text 'Set Baud rate to the selected value on

            SerialPort1.Parity = IO.Ports.Parity.None
            SerialPort1.StopBits = IO.Ports.StopBits.One
            SerialPort1.DataBits = 8 'Open our serial port
            SerialPort1.Open()
            btnConnect.Text = "disconnect"

            txtSN.Enabled = True
            btSend.Enabled = True
        End If

        If SerialPort1.IsOpen = True Then
            TextBox1.Text = TextBox1.Text & vbCrLf & "Process" & " : " & "connect success with " & SerialPort1.PortName & " / " & SerialPort1.BaudRate
        Else
            TextBox1.Text = TextBox1.Text & vbCrLf & "process" & " : " & "connect loss"
        End If
    End Sub

    Private Sub SerialPort1_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort1.DataReceived
        ReceivedText(SerialPort1.ReadExisting()) 'Automatically called every time a data is received at the serialPort
    End Sub

    Private Sub ReceivedText(ByVal [text] As String)

        If Me.txtOutput.InvokeRequired Then
            Dim x As New SetTextCallback(AddressOf ReceivedText)
            Me.Invoke(x, New Object() {(text)})
        Else
            Me.txtOutput.Text &= [text]
        End If

        ''compares the ID of the creating Thread to the ID of the calling Thread
        'If Me.txtSN.InvokeRequired Then
        '    Dim x As New SetTextCallback(AddressOf ReceivedText)
        '    Me.Invoke(x, New Object() {(text)})
        'Else
        '    Me.txtSN.Text &= [text]
        'End If
    End Sub


    Private Sub send_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btSend.Click
        'SerialPort1.WriteLine(txtSN.Text.Trim)
        SerialPort1.Write(txtSN.Text & vbCrLf)

        TextBox1.Text = TextBox1.Text & vbCrLf & " send command : " & txtSN.Text
        txtSN.Text = ""
    End Sub
End Class