unable to communicate with obd-II

Question

I am trying to communicate with ECUsim 2000 which is OBD-ll ECU simulator (link). Yet, responses I always receive from device are something like "??" or "?" (when I run programs like TouchScan or OBD Auto Doctor, they successfully reads data so device is working properly). I am sending comand in C# via

serialPort1.Write("010D\r")

and I am receiving signal in SerialPort's DataReceived event as

 message = "Data Received: " + serialPort1.ReadExisting();
 this.Invoke(new EventHandler(displayText));

I do not now what I am missing. Here is the full source code

private void Form1_Load(object sender, EventArgs e)
    {
        serialPort1.PortName = "COM3";
        serialPort1.BaudRate = 115200;
        serialPort1.Parity = System.IO.Ports.Parity.None;
        serialPort1.StopBits = System.IO.Ports.StopBits.One;
        serialPort1.DataBits = 8;
        serialPort1.Handshake = System.IO.Ports.Handshake.None;

        serialPort1.Open();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        if (serialPort1.IsOpen)
        {
            serialPort1.Write("010D\r");
        }
    }

    private void displayText(object sender, EventArgs e)
    {
        textBox1.AppendText(message + "\n");
    }

    private void serialPort1_DataReceived(object sender,      System.IO.Ports.SerialDataReceivedEventArgs e)
    {
        message = "Data Received: " + serialPort1.ReadExisting();
        this.Invoke(new EventHandler(displayText));
    }

Default communication settings of ECUsim 2000 are

Baud Rate: 115200 Data bits: 8 Parity: none Stop bits:1

protocol is ISO 15765-4 and there are two switches on the device which are protocol attribute CAN ID 29/11 bit and CAN Baud Rate 500 kbps/250kbps. Maybe, the problem are related with these such that there is no proper communication set.

Another question -> Is there a way to set protocol (like ISO 15765-4) in serial communication?

The ? characters are produced by Encoding.ASCII trying to convert nonsense back to a real ASCII character and giving up hope because the data contains values > 127. No serial port device ever uses its product number as the baudrate. — Hans Passant, Jun 05 '14 at 22:53
Sorry, I edited the Baud Rate as it is seen on the code. I think error is due to the interpreting received data — Gorkem Polat, Jun 05 '14 at 23:06
CAN doesn't use ASCII, it is not a text protocol. So don't use the SerialPort methods that return a string, use Read() instead. — Hans Passant, Jun 05 '14 at 23:28

score 1 · Accepted Answer · answered Jun 06 '14 at 18:52

There are two problems related with the code given.

1) There are two connector on the ECUsim 2000. One of them is type B USB port, other one is Diagnostic Link Connector (DLC). If one wants to get connected to device via type B USB port, baud rate is: 115200. If DLC is used, Baud Rate is most probably either 9600 or 38400. Here, connection is made through scan tool, therefore (for my case) baud rate 38400 worked for me.

2) As mentioned in the comment, In order to get data, Read() method of SerialPort must be used. It can be used as the following code:

int buffSize = 1024;
bool cont = true;
int count = 0;
byte[] bff = new byte[buffSize];
string returnVal = string.Empty;
count = serialPort1.Read(bff, 0, buffSize);
returnVal += System.Text.Encoding.Default.GetString(bff, 0, count);

unable to communicate with obd-II

1 Answers1