Hi Grumpy_Mike,
thanks for the answers!
Grumpy_Mike:
you can't damage the chip by programming it wrong.
Well you can if you have an output feeding into an arduino input and you program that pin to be an output. If then the external output and the arduino one are different levels you can damage the arduino pin.
With "other level" do you mean other voltage? So if I have only 5V everywhere can that be OK?
best regards
Andreas