I've been programming my ATmega328P's using USBasp programmer for a while. For my new project, I wanted to use 32.768kHz oscillator as an external clock, so I programmed the ATmega to appropriate fuses. Unfortunately, from this point on, I cannot communicate with the chip at all – avrdude tells me that target doesn't answer (rc=-1 error). After some research, I found some tips telling me to connect the oscillator (and capacitors) to chip's XTAL inputs, and then program the chip. I tried that, to no avail. Note that I also used avrdude's -B 2000 switch, that slows down the programming as much as possible – to 500Hz, so programming speed shouldn't be an issue.
In a desperate attempt to rescue chip, I tried Arduino as ISP, but the results were pretty much the same.
Questions:
-
How to rescue this particular ATmega? Is high voltage programmer the only way out of this? I don't have one, so other options are welcome.
-
For the future: how should I program slow clock fuses so that I avoid this problem? It doesn't make sense for me – if programmer doesn't work with such fuses, why is there such a fuse setting in the first place?
Best Answer
Even when fused to use a crystal, the ATmega328P will accept a clock signal injected into XTAL1 when being programmed by ISP. The USBasp does not provide such a signal so you will need to set up another circuit to generate a clock signal fast enough for programming.
The programmer should work with such a slow clock assuming the programmer uses a slow clock as well. Verify that the crystal operates normally.