ATmega169 Puzzle

Well a few days ago I was having trouble setting up a simple spi interface.
 Whenever I would try to lower the chip select lines of my devices the 169
would try it and then give up and reset itself.

I finally figured out that the problem was the pin I was trying to use.  I
was using PINB0 and PINB4 as chip select lines.  B4 was the one giving me
trouble so I switched it to B5 and the problem was solved.  Now I'm
noticing that PINB6 does the same thing.

What is going on here???

Joel wrote:
> Well a few days ago I was having trouble setting up a simple spi interface.
>  Whenever I would try to lower the chip select lines of my devices the 169
> would try it and then give up and reset itself.
> 
> I finally figured out that the problem was the pin I was trying to use.  I
> was using PINB0 and PINB4 as chip select lines.  B4 was the one giving me
> trouble so I switched it to B5 and the problem was solved.  Now I'm
> noticing that PINB6 does the same thing.
> 
> What is going on here???

Maybe you have interrupts enabled (by accident) on those pins, and no 
valid handler ?

> =A0Whenever I would try to lower the chip select lines of my devices the 1=
69
> would try it and then give up and reset itself.

Single-step; there is no reason why you shouldn't be able to use any
GPIO as your SPI _SS. Also check that your circuit is not wired in
some funky way whereby asserting _SS was shorting out the power
supply.

larwe wrote:
>>  Whenever I would try to lower the chip select lines of my devices the 169
>> would try it and then give up and reset itself.
> 
> Single-step; there is no reason why you shouldn't be able to use any
> GPIO as your SPI _SS. Also check that your circuit is not wired in
> some funky way whereby asserting _SS was shorting out the power
> supply.


This may be the perfect time to leave the embedded/digital world for a 
minute, hang a scope on it and take a look.

-- 
Regards, Joerg

http://www.analogconsultants.com/