Modbus rtu in visual basic (vb.net)

Public Function SendFc3(ByVal address As Byte, ByVal start As UShort, ByVal registers As UShort, ByRef values As Short())

        Dim flag As Boolean = False
        'Ensure port is open:
        If (Sp.IsOpen) Then

            'Clear in/out buffers:
            Sp.DiscardOutBuffer()
            Sp.DiscardInBuffer()
            'Function 3 request is always 8 bytes:
            Dim message As Byte() = New Byte(7) {}
            'Function 3 response buffer:
            Dim response As Byte() = New Byte((5 + 2 * registers) - 1) {}
            'Build outgoing modbus message
            BuildMessage(address, CByte(3), start, registers, message)
            'Send modbus message to Serial Port:
            Try

                sp.Write(message, 0, message.Length)
                'Evaluate message:
                If (GetResponse(response, sp, values)) Then
                    flag = True
                End If

            Catch err As Exception
                modbusStatus = "Error in read event: " + err.Message
                flag = False
            End Try
        Else

            modbusStatus = "Serial port not open"
            flag = False
        End If
        Return flag

    End Function

Public Sub BuildMessage(ByVal address As Byte, ByVal type As Byte, ByVal start As UShort, ByVal registers As UShort, ByRef message As Byte())

       'Array to receive CRC bytes:
       Dim CRC As Byte() = New Byte(2) {}

       message(0) = Byte.Parse(address)
       message(1) = Byte.Parse(type)
       message(2) = Byte.Parse(start >> 8)
       message(3) = Byte.Parse(start)
       message(4) = Byte.Parse(registers >> 8)
       message(5) = Byte.Parse(registers)

       GetCRC(message, CRC)
       message(message.Length - 2) = Byte.Parse(84) 'CRC(0)
       message(message.Length - 1) = Byte.Parse(10) 'CRC(1)

   End Sub

Public Function GetResponse(ByRef response As Byte(), ByRef spModbus As SerialPort, ByRef values As Short())

        Dim i As Integer = 0
        'Thread.Sleep(300)
        While (spModbus.BytesToRead <> 0)
            response(i) = Byte.Parse(spModbus.ReadByte())
            'Thread.Sleep(200)
            i += 1
            'Application.DoEvents()
        End While

        'Verifico il messaggio
        If (CheckResponse(response)) Then

            'Ritorno il valore dei registri richiesti
            For i = 0 To ((response.Length - 5) / 2) - 1

                response(i) = response(2 * i + 3)
                response(i) <<= 8
                response(i) += response(2 * i + 4)
                values(i) = response(2 * i + 3)
                values(i) <<= 8
                values(i) += response(2 * i + 4)

            Next

            Return True

        Else

            Return False

        End If

    End Function