SerialPort read/write using same opened port

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I am trying to use SerialPort object to listen for incoming data and send outgoing data.

Doing each other separately, it is working well - I can send or receive with no issues. The problem happens when I want to make this port available for both operations.

What I do is this (In a dedicated thread):

private void SerialCommunicationsListen(SerialPort serialPort)
{
while (true)
{
string val = serialPort.ReadLine();
// do some code with val
}
}

This is the listener. 2nd thing I'm doing is this for sending data out:

public void SendMessage(SerialPort port, string message)
{
port.Write(message);
}

Both are using the same SerialPort object. The thing is that if I call "SendMessage" when the listener is up, the listener receives the data instead of the device, and if it is down, the device is the one receiving it.

What am I doing wrong here? I want to do both transmit and receive from the device on the same port.

Posted 17-Apr-15 23:04pm

impeham

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OriginalGriff · Accepted Answer · 2015-04-17T23:42:00

Solution 1

Don't.
The problem is probably that ReadLine is a blocking operation - it doesn't return until a complete line together with line end character(s) has been received by the serial port - so your code can't do anything else until that happens.

Instead, use the SerialPort.DataReceived event[^] and buffer up the data yourself in a stringbuilder yuntiul you have a complete line. You can then process the line.
That way, your code isn't sitting waiting for data all the time and doing nothing else!

Posted 17-Apr-15 23:42pm

OriginalGriff

Comments

impeham 18-Apr-15 6:12am

won't this solution create the same problem? when i write to the port, my listener is the one receiving the data (and i assume will be the one that will get the raised event) instead of the device...

OriginalGriff 18-Apr-15 6:33am

Check your port with Hyperterminal or similar - it sounds like you have an echo coming back from the device (some do that if they receive text so the user can read it as he types)

impeham 18-Apr-15 7:18am

Thanks - i found it :)
working well now.