I was looking at the UNO Rev3 schematic and noticed there is a 1M ohm resistor bridging XTAL1 and XTAL2, before the crystal. What purpose does that resister (R2) serve?
gerg: I was looking at the UNO Rev3 schematic and noticed there is a 1M ohm register bridging XTAL1 and XTAL2, before the crystal. What purpose does that resister (R2) serve?
Actually a Uno does not use a crystal resonator for the 328p chip, but rather a ceramic resonator. I'm not sure what the reason for the 1M ohm resistor is. The 328p datasheet does not make any reference to it's need, but perhaps some AVR application note might? So I suspect the leaves two choices, either it's a recommendation of the ceramic resonator manufacture for more consistency in oscillator start-up timing or more stable operation (but I rather doubt it) or it's something the Arduino found that was needed to get some rated RFI testing/approval inspection passed. I'd vote the latter reason, but again I don't know for a fact.