不會的就放這邊

    Public Function AsciiStringToHexString(ByVal asciiString As String) As String
        Dim ascii() As Byte = System.Text.Encoding.Default.GetBytes(asciiString)
        Dim count As Integer = ascii.Length
        Dim hexArray(count - 1) As String
        For idx As Integer = 0 To count - 1
            hexArray(idx) = ascii(idx).ToString("x2")
        Next
        Return String.Join(" ", hexArray)
    End Function


    Public Function HexStringToAsciiString(ByVal hexString As String) As String
        Dim array() As String = hexString.Split(New Char() {" "c}, StringSplitOptions.RemoveEmptyEntries)
        For idx As Integer = 0 To array.Length - 1
            array(idx) = Chr(CInt(String.Format("&h{0}", array(idx))))
        Next
        Return String.Join(String.Empty, array)
    End Function


    Private Sub tbxASCII_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tbxASCII.TextChanged
        If Me.ActiveControl Is sender Then
            tbxHex.Text = AsciiStringToHexString(tbxASCII.Text)
        End If
    End Sub

    Private Sub tbxHex_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tbxHex.TextChanged
        If Me.ActiveControl Is sender Then
            tbxASCII.Text = HexStringToAsciiString(tbxHex.Text)
        End If
    End Sub
End Class