16u2 and the reset pin

I'm trying to reprogram the onboard 16u2 to become "first-class" programmers for the onboard target chip (in my case, the mega2560 and mega328p). I've jumpered SCK/MOSI/MISO from the U2 breakout to the target breakout. Most of the code is working, but I've encountered a hardware obstacle, the capacitor between D7 on the U2 and RESET on the target chip. The capacitor, I guess, provides a hardware "bounce" to the reset pin.

But I need the U2 to hold RESET down during SPI programming.

I'm speaking of capacitor C7 on the mega schematic and C5 on the uno.

Any thoughts how to get around it?

The only thing I can think of is to solder over the capacitor.. this could cause trouble if the reset button is held down while the U2 is trying to program (might burn out the U2?), but I guess I can live with that. Any other ideas?

Also: can anyone provide a photo of the mega2560 and uno, showing me physically where the troublesome capacitors are? (So I can trying soldering over them.)


Can’t you just ignore it and have the 16U2 control the Reset line directly? It is only pulled up by 10K resistor.

How are you suggesting I hold it down? I can keep D7 low, but the capacitor blocks DC, so even though the pullup is "only" 10k, it comes up pretty quickly. Certainly not long enough to program the chip (which requires ~20ms settling time before programming anyway).

More precisely: 100nF capacitor and 10K resistor should yield a time constant of 1ms.