I am developing some firmware that needs to send binary data to a .NET app
via rs232.  I have created a test .NET app that uses the SerialPort class to
read the data, however it is erroneously doing a replacement on the value
0xFF to be 0x3F (the default ParityReplace character).  I am specifically
setting Parity to None and ParityReplace = 0 to stop this, however it
continues to replace the character.

I believe this might be a bug in the SerialPort class itself, because I can
use DOS or hyperterminal to view the incoming data, and neither appears to
replace the 0xFF with 0x3F (which is '?').

Here is the code I am testing with.  Hook up a serial cable from COM1 to
COM2, run the app, press the buttin, and send some 0xFFs from COM1->COM2 to
test.  Other characters appear to work fine.

//***************************************

using System;
using System.Windows.Forms;
using System.IO.Ports;

namespace WindowsApplication1
{
    public partial class Form2 : Form
    {
        private SerialPort _port;

        public Form2()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (_port == null)
            {
                _port = new SerialPort("COM2", 19200, Parity.None, 8,
StopBits.One);
                _port.ParityReplace = (byte)'\0';
                _port.ReadTimeout = 500;
                _port.DataReceived += new
SerialDataReceivedEventHandler(_port_DataReceived);

                _port.Open();
            }
            else
            {
                _port.Close();
                _port.Dispose();
                _port = null;
            }
        }

        void _port_DataReceived(object sender, SerialDataReceivedEventArgs e)
        {
            this.Invoke(new Action<int>(handleData), 0);
        }

        private void handleData(int dummy)
        {
            char[] c = new char[_port.BytesToRead];
            _port.Read(c, 0, c.Length);

            for (int i = 0; i < c.Length; i++)
            {
                textBox1.Text += ((int)c[i]).ToString("x") + " " + c[i] +
"\r\n";
            }
        }
    }
}

Hi David,

I don't know, but I will take a look later today.  Of course, if there is a
bug I cannot fix it (and a fix will be a while coming, I suspect).  However,
if I verify the problem I will submit it.

In the meantime, you can download DesktopSerialIO from my homepage to get
you going.

David,

BTW, post the syntax that you are using to read the data (just in case).

Dick

Hi Dick,

thanks for looking into it.  I believe I have found more information which
might be valuable.  It seems to read correctly if I use the Read(byte[]...)
instead of Read(char[]...).  It seems the Read with char[] ignores the
ParityReplace or something.  I might take a peek in SerialPort with reflector
later and see if I see the problem (if it's not off in native land).

The code I posted is everything I have (other than the firmware that sends
the data).  All I do is send the hex value and char value to a textbox, and
the value is 3F instead of FF.  I have progressed beyond this since I
realized the byte[] overload worked.

Show quoteHide quote

I wrote the following as a test (modified the code for the simple terminal
program on my web site):

Dim Count As Integer = SerialPort.BytesToRead

Dim Buffer(0 To Count - 1) As Byte

Dim Text2Display As String

SerialPort.Read(Buffer, 0, Count)

For I As Integer = 0 To Buffer.GetUpperBound(0)

Text2Display += Hex(Buffer(I)) & " "

Next

Debug.WriteLine(Text2Display)

If Text2Display IsNot Nothing Then _

DefInstance.txtTerm.BeginInvoke(New DisplayData(AddressOf Display), New
Object() {Text2Display})

This works fine, with no error, nor any incorrect data displayed.  All hex
characters are shown.  As you see it uses the Read method.

Dick,

please try your sample using a char[] instead of byte[].

Here is the simplest example code I could derive which shows the problem. 
Just connect a serial cable between COM1 and COM2, run the code, and double
click the form.  You will see 0x3f  :  ?  when you should see 0xFF  :


Here is the code:
using System;
using System.Windows.Forms;
using System.IO.Ports;

public class Test : Form
{
    static void Main()
    {
        Application.Run(new Test());
    }

    private SerialPort _port;
    public Test()
    {
        this.DoubleClick += new System.EventHandler(this.Test_DoubleClick);

        _port = new SerialPort("COM2", 9600, Parity.None, 8, StopBits.One);
        _port.DataReceived += new
SerialDataReceivedEventHandler(_port_DataReceived);
        _port.ParityReplace = (byte)'\0';

        _port.Open();
    }

    void _port_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        this.Invoke(new Action<int>(handleData), 0);
    }

    void handleData(int dummy)
    {
        char[] buf = new char[1];

        _port.Read(buf, 0, 1);

        MessageBox.Show("0x" + ((int)buf[0]).ToString("x") + "  :  " +
buf[0]);
    }

    private void Test_DoubleClick(object sender, EventArgs e)
    {
        SerialPort p = new SerialPort("COM1", 9600, Parity.None, 8,
StopBits.One);
        p.ParityReplace = (byte)'\0';
        p.Open();

        char[] buf = new char[] { (char)0xFF };
        p.Write(buf, 0, 1);

        p.Close();
        p.Dispose();
        p = null;
    }
}
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