AVR-Chat

At 06:21 PM 6/23/2004 +0000, Ken wrote:

>I'm new to AVR's and just want to know what to do with unused I/O 
>lines.  I assume I would set them to inputs, enable the internal 
>resistors and tie them to ground.  Is that right?

You're drawing extra current that way, pulling them up internally, and down externally.

What happens if you accidentally program them to output high?

This question usually evokes a "religious" discussion, as there are a couple ways to handle it, some wrong, some right.

What you don't want to do, is leave them as inputs floating, or outputs tied to the opposite state they are driven to. Both of these cases will draw excess current, and the first one can cause other problems.

I would advise to set them input, pulled up, and then add a resistor pad connected to each one, in case you want to use them for something later.

You could also set them to output low, or high, in the same case. 

Tying them hard to ground or VCC could get you in trouble.