Imports System.IO.Ports
Public Class Form1
    Dim simvol As Integer
    Dim com1 As IO.Ports.SerialPort = Nothing
    Function ReceiveSerialData() As Integer
        Dim simvol2 As Integer
        simvol2 = com1.ReadByte()
        Return simvol2
    End Function
    Sub GetSerialPortNames()
        For Each sp As String In My.Computer.Ports.SerialPortNames
            ListBox1.Items.Add(sp)
        Next
    End Sub
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        TextBox1.Multiline = True
        TextBox1.ScrollBars = ScrollBars.Vertical
        TextBox1.WordWrap = True

        GetSerialPortNames()
    End Sub

    Sub openuart(poort As String)
        com1 = My.Computer.Ports.OpenSerialPort(poort)
        With com1
            com1.BaudRate = 9600
            com1.Parity = IO.Ports.Parity.None
            com1.DataBits = 8
            com1.StopBits = IO.Ports.StopBits.One
            com1.ReadTimeout = 3000
        End With
        If com1.IsOpen Then Label1.Text = "Порт открыт" Else Label1.Text = "Порт заблокирован. Возможно, открыт в другой программе"
    End Sub

    Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox1.SelectedIndexChanged
        Dim cursoor As Long
        openuart(ListBox1.SelectedItem)
        Do
            simvol = ReceiveSerialData()


            If simvol = Nothing Then
            Else
                cursoor = TextBox1.SelectionStart
                If CheckBox1.Checked = True Then
                    TextBox1.Text &= Str(simvol)
                Else
                    TextBox1.Text &= CStr(CChar(CStr(simvol)))
                End If
                TextBox1.SelectionStart = cursoor
            End If
            Application.DoEvents()
        Loop
    End Sub