AVR-Chat

On Wed, Aug 31, 2005 at 12:22:16PM -0500, Thomas Keller wrote:
> 
>   Perhaps I am missing something, here.  AVR processors have
>   selectable pull UP resisotrs on each and every digital I/O pin.
>   Since a low voltage is a logic 1, you don't need "pull down"
>   resistors on AVR inputs.

Uh, "low voltage is a logic 1"? Maybe low is 1 if none is 0.

If the external source requires a load to drain its charge (and
therefore voltage) then you need a pull-down resistor. When the external
source is a current source.

If the external source isn't really a source but a switch or open
collector output then you need a pull up resistor to feed it, that one
can detect when it closes its circuit.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
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Whom computers would destroy, they must first drive mad.