c# serial port data loss

Question

I have written a C# program to receive data on COM2 port. The baud rate is set as 115200. The sender is sending the data at 115200bps. My program is losing a few bytes ocassionally. I am calling ReadByte method to read the data in a while(true) loop from the com port.

I have few questions:

When the baud rate is set high, should I expect to lose data? if yes, why?
I am setting the readbuffer size as 100*1024*1024. Does this set the serial driver buffer size to 100*1024*1024?

Any thoughts on how to debug this problem?

What do you do besides ReadByte inside the while loop? How long does the processing take? — Ian Mercer
After reading the byte from the Serial port, it would be put it in to a buffer until the buffer reaches 12 bytes. once it reaches 12 bytes, it would be compared against the defined commands which would take very less time. — user209293
You should ensure you're using flow control if you're not already doing so. — Jason Down
The answers for this question may also be helpful: stackoverflow.com/questions/222455/… — Jason Down

Andy Andy · Accepted Answer · 2010-12-31T12:22:35

A receive buffer size of 100*1024*1024 is HUGE! I would seriously doubt you need this size at all, and certainly not for the actual serial port buffer.

It could be that you are overflowing the physical receive buffer of the receiver, so you may have to look into using flow control. This will effectively enable your Receiver to say to your Transmitter "Hang on, stop sending for a while, let me deal with what I have first."

Hardware flow-control is (commonly) utilised through the RTS (Request To Send) and CTS (Clear To Send) pins.

Take a look at this article, which explains a bit more about it.

I would personally recommend leaving the ReceivedBytesThreshold property of the serial port to its default value of 1, and then handling the DataReceived event. Who knows, maybe tomorrow you will need to read a message of 20 bytes, or perhaps 5 bytes. Maybe you will need to read messages of variable length in the future? Leaving the threshold at 1 will mean that you can handle any and all bytes that will be received, now and in the future.

This threshold will mean the event will fire when there is at least 1 byte in the buffer. There maybe more, and probably will be. Note that it does NOT necessarily mean it will fire for every single byte received. On each event, you need to check the BytesToRead property and read this many into your own buffer.

It is worth repeating that the event will NOT necessarily fire for every single byte received.

Also, it is best to do as little as possible within the DataReceived event handler. Read in any bytes received into your buffer, and perhaps add completed messages into a queue for further processing, but do little else.

Also note that the standard maximum spec of RS232 is a speed of 19200 baud and a length of cable of 50 feet. Anything above that is undefined. Higher speeds generally need better cable (lower capacitance) and shorter cable lengths. Make sure it is screened and not running near other 'noisy' items such as motors, motor inverters, live cables etc.

c# serial port data loss

2 Answers