AVR-Chat

I have a board with an AVR driving a LS chip directly,
and it works fine.  But I had problems with source
code like this:
  PORTA = PINA | 0x01;
It seems that under certain conditions PORTA is not
equal to PINA.  I modified the code like this:
  PORTA = PORTA | 0x01;
and it solved the problem.

The first thing that comes to mind when you say that
"AVR was unable to pull the input on the logic chip
completely low" is that AVR pin was actually set as
input.  That way you would be pulling high the pin by
using the internal pull-up.  But you woudn't be able
to pull down the pin because it just would enter into
high impedance state.




Regards

Jose



> kernels_nz wrote:
> > Hi Guys,
> > 
> > Ive had two different boards lately give a lot of
> trouble, both had 
> > OUTPUTS on AVR chips connected directly to inputs
> on 74HC and 74LS 
> > logic chips. 
> > 
> > Looking at it with my scope, it appeared that the
> AVR was unable to 
> > pull the input on the logic chip completely low ?
> It would pull it to 
> > around 1 to 3 volts for a low output.
> > 
> > I did ensure that the pins were set up as OUTPUTS,
> nothing else 
> > weird. 
> > 
> > Both problems were solved by connecting 100k
> resistors from the input 
> > pins on the logic chips to ground.
> > 
> > Any ideas ? Im sure it will be obvious as soon as
> someone points out 
> > the obvious, but it's got me beat.
> > 
> > Cheers
> > Hein B
> > Andante Technology
> > Auckland
> > New Zealand.
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> >  
> > Yahoo! Groups Links
> > 
> > 
> > 
> >  
> > 
> > 
> 
> -- 
> -------------------------------------------------
> Dennis Clark          TTT Enterprises
> www.techtoystoday.com
> -------------------------------------------------
> 
> 
>  
> Yahoo! Groups Links
> 
> 
>     AVR-Chat-unsubscribe@yahoogroups.com
> 
>  
> 
> 
> 


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