The ATtiny85 datasheet specifies an absolute maximum negative voltage for any pin of -0.5 volts relative to ground.
Consider this partial schematic:
MOSI and MISO are the respective ATtiny85 pins and the CLOCK terminal is connected to the coil of a lavet stepper motor - which means it's just an electromagnet coil.
It works, but when I had the outputs on a scope to examine some of the timing, I happened to notice a negative going spike as the output is turned off, despite the presence of the flyback diode. I quickly realized that the magnitude of the spike is the forward voltage of the diode - in this case, 1 volt.
The question I have now is, does that absolute maximum (actually, absolute minimum in this case) rating apply to pins configured as outputs set to LOW?
I can replace the 1N4148s with Schottky diodes with a forward voltage of only 0.5 volts... but is it worth bothering with?