AVR-Chat

The LS might require too much drive for a CMOS output, but the AVR's can 
drive LED's directly so they have lots of drive current.  The HC part is 
a CMOS part and should pose no problems to the AVR.  Many parts have 
weak pull up or pull downs on them.  Is is possible to program those on 
when there is an output and create a problem?

DLC

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.
> 
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>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 

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Dennis Clark          TTT Enterprises
www.techtoystoday.com
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