AVR-Chat

On Sun, 02 Sep 2007 12:44:43 -0000
 "wd0e" <jim@coloradosatellite.com> wrote:
> We have a pair of ATMEGA128s talking to each other using
> SPI.  The
> slave is not always powered on.  The problem is when Vcc
> to the slave
> is off it gets partially powered by the SPI lines.
> 
> It appears we could isolate them with optoisolators. But
> is there a
> better/cheaper/smaller way?
> 
> Jim
> 
You could use a FET in each line with the pull-up powered
by  the local power for the second micro. That should be
smaller, cheaper, and lower power than opto isolators.

Jim Wagner
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