Possible bug with SerialPort Parity.None and/or ParityReplace

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  • Start date Start date
G

Guest

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).ToString("x") + " " + c +
"\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.

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.
 
David,

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

Dick

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.
 
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.
 
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.

--
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
Edition,
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
2006.
See www.hardandsoftware.net for details and contact information.
 
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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