I have an Arduino Mega 2560 that is resetting every 32 seconds if the serial monitor is not attached. Just before it resets, there is a flash of TX, then it goes. If ther serial monitor is attached it runs forever. Clearly I can't use the serial monitor to debug this so am clutching at straws as to what is happening.
Having eliminated all code and uploaded an empty sketch, no includes etc., the board still exhibits the reset. However, I have an Adafruit Ultimate GPS attached to the GND, 5V, TX1 and RX1 pins. When I remove it the resets stop. But with it attached and the serial monitor attached to the board, the resets also stop, even with an empty sketch. Spooky.
So, is it possible the GPS unit is filling a receive buffer, even if the serial port isn't set up to receive? I still have a problem that while I'm clearing and logging the GPS data, the resets are still at a regular 32 seconds, thus the reason I'm working on it still.
Note: The flash of TX no longer shows up with the empty sketch.