How to avoid Attiny84 being powered on by a pulled up data line?
This happens because there are internal protection diodes on the GPIO pins so any voltage that comes in is shunted to the internal power rail...



Even though these are little diodes, this chip uses so little power that it is often enough to run it. This is the source of one of the top-10 hardest bugs I've ever hard to find!

Method #1 - Pull ~RESET Low

As long as the voltage on the ~RESET pin is less than 0.2*Vcc, then the chip will stay in a reset condition and not running. 



You can connect the ~RESET pin to the power supply pin and use a pull-down resistor to keep the ~RESET pin below the threshold when there is no active power supply.  Note that you need the pull-down because there is an internal pull-up on the ~RESET pin. 







simulate this circuit &ndash; Schematic created using CircuitLab

This method wastes a little current, but will keep the chip in a reset state when it is not actively powered.

Keep in mind that there will be a voltage drop across the diode.

Method #2 - Isolate Input Pins







simulate this circuit

Here we use the power supply to enable the input pin. If there is no voltage coming from the power supply, no significant current to flow into the input pin.