I have a very basic circuit built around an ATTiny85.
Right now, I am not using the ADC, but have plans to add that functionality in the future.
p. 123 of the complete data sheet says,
The voltage reference for the ADC may be selected by writing to the REFS[2:0] bits in ADMUX. The VCC supply,
the AREF pin or an internal 1.1V / 2.56V voltage reference may be selected as the ADC voltage reference. Optionally
the internal 2.56V voltage reference may be decoupled by an external capacitor at the AREF pin to improve
I have the attached schematic, with C9 decoupling the AREF pin.
However, when I attempt to program the chip via ISP (AVRISP mkii), it fails to enter programming mode. When I remove C9, the programming process works normally. I understand that C9 is loading down the PDI line, causing programming to fail. How then, am I to follow the recommendation in the data sheet to decouple the AREF pin? Is that not possible for actual ISP (i.e., would I need to program the board on a carrier w/o the cap, and then transfer it to the final assembly? It seems like adding a resistor in series w/ the decoupling capacitor (a la the other pins) would defeat the purpose of the capacitor in the first place.