Private Sub btnsend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnsend.Click
        Dim sj() As Byte
        Dim sj_txt As String
        Dim i As Integer
        sj_txt = txtsend.Text
        If txtsend.TextLength Mod 2 = 0 And txtsend.TextLength <> 0 Then '检验16进制字符串长度
            ReDim sj(Len(sj_txt) / 2 - 1)
            For i = 0 To Len(sj_txt) - 1 Step 2
                sj(i / 2) = Val("&H" & Mid(sj_txt, i + 2, 2))
            Next
            If RS232.IsOpen Then
                'Dim si = Convert.ToBase64String(sj)
                RS232.WriteLine(sj_txt)
            Else
                MsgBox("端口未打开或被占用！")
            End If
        End If
    End Sub
上述代码如何才能实现将文本框中输入的数据按照16进制发送？