Question

I am new to serial communication. I have read a fair few tutorials, and most of what I am trying to do is working, however I have a question regarding serial communication with C#. I have a micro controller that is constantly sending data through a serial line. The data ist in this format:
bxxxxixx.xx,xx.xx*
where the x’s represent different numbers, + or – signs.
At certain times want to read this information from my C# program on my PC. The problem that I am having is that my messages seem to be split in random positions even though I am using
ReadTo(“*”);
I assumed this would read everything upto the * character.
How can I make sure that the message I recieved is complete?

Thank you for your help.

    public string receiveCommandHC()
    {

        string messageHC = "";
        if (serialHC.IsOpen)
        {
            serialHC.DiscardInBuffer();
            messageHC = serialHC.ReadTo("*");

        }
        return messageHC;
    }

Answer 1

You’ll nearly always find in serial comms that data messages (unless very small) are split. This is mostly down to the speed of communication and the point at which you retrieve data from the port.

Usually you’d set your code to run in a separate thread (to help prevent impacting the performance of the rest of your code) which raises an event when a complete message is received and also takes full messages in for transmission. Read and write functionality is dealt with by worker threads (serial comms traffic is slow).

You’ll need a read and a write buffer. These should be suitabley large to hold data for several cycles.

Append data read from the input to the end of your read buffer. Have the read buffer read on cyclicly for complete messages, from the start of the buffer.

Depending on the protocol used there is usually a data start and maybe a data end indicator and somewhere a message size (this may be fixed, again depending on your protocol). I gather form your protocol that the message start character is 'b' and the message end character is '*'. Discard all data preceeding your message start character (‘b’), as this is from an incomplete message.

When a complete message is found, strip it from the front of the buffer and raise an event to indicate its arrival.

A similar process is run for sending data, except that you may need to split the message, hence data to be sent is appended to the end of the buffer and data being sent is read from the start.

I hope that this helps you in understanding how to cope with serial comms.

As pointed out by Marc you’re currently clearing your buffer in a way that will cause problems.

edit

As I said in my comment I don’t recognise serialHC, but if dealing with raw data then look at using the SerialPort class. More information on how to use it and an example (which roughly uses the process that I described above) can be found here.