AVR-Chat

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?

IF it were me I would leave them untied to any external connections, just
program them as inputs with the pullups. That way you can always connect
something to them in a pinch after the board is built and you suddenly
discover you need an input or output line.

Al Welch

-----Original Message-----
From: Ken [mailto:kenlem@maine.rr.com]
Sent: Wednesday, June 23, 2004 11:22 AM
To: AVR-Chat@yahoogroups.com
Subject: [AVR-Chat] Unused I/O lines


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?





Yahoo! Groups Links

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.

>just program them as inputs with the pullups.

You can do that! Sweet. The more I play with the AVR's, the more I 
like them.  Sorry if it seems like a simple question. I'm a software 
guy mostly and have only begun to explore hardware.

Ken
http://www.speechchips.com


--- In AVR-Chat@yahoogroups.com, "Al Welch" <alwelch@a...> wrote:
> IF it were me I would leave them untied to any external 
connections, just
> program them as inputs with the pullups. That way you can always 
connect
> something to them in a pinch after the board is built and you 
suddenly

> discover you need an input or output line.
> 
> Al Welch
> 
> -----Original Message-----
> From: Ken [mailto:kenlem@m...]
> Sent: Wednesday, June 23, 2004 11:22 AM
> To: AVR-Chat@yahoogroups.com
> Subject: [AVR-Chat] Unused I/O lines
> 
> 
> 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?
> 
> 
> 
> 
> 
> Yahoo! Groups Links

OK. Unconnected and internal pull up resistors enabled it is then.   
Thanks for the answer. Hope I haven't started anything. :)

Ken
http://www.speechchips.com

--- In AVR-Chat@yahoogroups.com, David VanHorn <dvanhorn@c...> wrote:
> 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.