Arduino restarting when serial over USB is read

Question

I have a timer application running on an Arduino Uno. Occasionally an interface is connected to it through USB to read the state of the timer. For development purposes it is read through the rs-232 emulation over USB.

The problem is that the Arduino seems to restart every time the serial reading is started on the remote side.

There is no voltage drop on either the 5V or 3.3V rails indication a brown out or crash.

Is this known behaviour and if so is there anything that can be done to prevent it?

Answer 1

Auto resetting when communicating through COM is the default behaviour in recent UNO's. If you have the liberty to modify your hardware you just have to pull the "RESET" pin to low, you can do this by setting a capacitor between RESET and GND. Alternatively there is this post about some guy facing the same issue.

http://wp.yellowkazoo.com/?p=177

Answer 2

Note the Reset is the desired feature of the UNO, as to synchronize the Boot Loader with avrdude. This is caused by the change of DTR pin when the application connects to the COM port.

Perhaps you can alter your application that is reading the COM port, as not to assert DTR. Thereby not toggling reset pin of the Arduino.