AVR won't exit reset -- Zapped?
Hardware: ATMEGA128RFR2, mounted on a custom board (no socket).
My colleague programmed a board (ISP) and verified the load. He then disconnected the board (power cable, comms cable, programmer cable) and carried the board (mounted on a plate) across the room for further testing. When he got to his other bench, he plugged in power and comms. Upon application of power, the microcontroller entered reset mode - and did not exit.
Note, the ATMEGA128RFR2 has a pin that indicates when it is in reset mode (pin 13 = rston). We have a current limited LED connected to this pin that lets me know when the chip is in reset mode. We have verified that the actual reset pin (pin 12) is high (i.e., NOT commanding the chip to enter reset mode).
As unlikely as it seems, I suspect some kind of ESD event - simply because I can't think of another reason why the chip would stop functioning over the course of 30 or so seconds.
It is possible he unplugged the programmer (AVRISP mk2) while the board was powered. Could that have had some permanent negative impact on the chip?
The chip is configured to use an external crystal. If the crystal somehow got damaged, and stopped oscillating, would that force the chip into reset mode?