SerialPort.DataReceived with USB TO COM cable act different then physical com

Question

My C# desktop class library communicates with COM serial port.
The com is not real com, it is a USB to COM cable connected to USB to COM on another computer, the other computer uses a simulator to send data.

This solution works fine and then port opens successfully:

serialPort.Open();
if (serialPort.IsOpen)
{
   serialPort.DataReceived += new SerialDataReceivedEventHandler(serialPort_DataReceived);
}

void serialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
  try
  {
     var length = serialPort.BytesToRead;
     byte[] buffer = new byte[length];
     serialPort.Read(buffer, 0, length);
     for (int i = 0; i < buffer.Length; i++)
     {
        System.IO.File.AppendAllText(@"c:\TestLogging.txt", string.Format("[Time = {0}]  Data was received from serial port !", DateTime.Now));         }
     } 

The simulator send data all the time, and I receive the data in my class, BUT i dont receive it all the time, i see printing of 1 line every 30 seconds - although it suppose to print all the time!

What is weird - If i place break point in the line var length = .. then i see a the prints for the time i was halting on the break.. the data transferred seems to be "cached" and when i hit "Play" I receive the data but only for the time i was pausing the process.

Answer 1

I think you're too late registering the DataReceived eventhandler there. You should register to it before you open the port:

serialPort.DataReceived += new SerialDataReceivedEventHandler(serialPort_DataReceived);
serialPort.Open();
if (serialPort.IsOpen)
{

}

Answer 2

Try connecting your machines using HyperTerminal and check if the communication works. If it does, then it's your application's fault (double-check serialport settings). Otherwise it's probably the cable or the port itself.

Are you sure you're not getting any faulty data? Have you subscribed to SerialPort.ErrorReceived event handler? If you catch some SerialError.Frame errors there, then you probably have a faulty cable or the port is broken, or there are some conditions that are jamming the comunication (not vary likely but it can happen, for example if there is some strong source of power near by, for example an inverter).

Answer 3

OK, what is the problem ?
I am using USB to COM cable, and not true COM port.
The behavior of data receiving event from SerialPort is different .
I listen and catch the data event, but instead of getting array of bytes (as in real COM) - I receive every time a single byte (array in size of 1)..
Meaning: On DataReceived event when working with USB to COM port: i get this: 1-1-1-1-1-1 each DataReceived event give me 1 byte.
Real physical COM .DataReceived event give me: 5-30-42 etc.. Array of bytes
So my solution when working on USB to COM ports (some might call it "virtual COM port") I need to check if serialPort.BytesToRead is bigger then X, then i actually do

if (serialPort.BytesToRead > 2) //I dont want to get it 1-1-1.. want to get it atleast 2-2-2-2
    serialPort.Read(buffer, 0, length);

Since serialPort.BytesToRead will tell me how many bytes are in current chunk, and Read. in my terms will get the buffer and clean it.