AVR-Chat

Graham,

Thanks.  But my explanation symantecs are probably a source for confusion...  

In this case, the adc renders readings that coorespond with an effective VREF of 5V.  And no combination of REFSx commands will get the device to behave against a scale of anything other than 5V.  That's the problem.  

Call it failing to recognize the external Vref, or whatever wording would be better, the problem is the same.  The top end of the ADC divider chain works as if there is 5V there - no matter what the code says.

It's not a hardware failure.  The device/code behaves the same in Proteus - and while I will buy the case that the actual hardware can fail with incorrectly applied voltages, the virtual version probably does not suffer from the same potential smoke issues.

I really cannot understand how something so basic and simple like this can fail to work.  Making me lose my mind...  


From: ecros_technology 
Sent: Friday, January 22, 2010 8:42 PM
To: AVR-Chat@yahoogroups.com 
Subject: [AVR-Chat] Re: Vref on ATTiny861a


  
--- In AVR-Chat@yahoogroups.com, "Jeff Blaine AC0C" <keepwalking188@...> wrote:

> Can you expand a bit more?
> ... Because the device did not
> seem to recognize the 4.0v bandgap
> ref, I put this in to see if varying
> the Vref would be reflected in
> different ADC readings. It does not. 

Well, the device "not recognizing" an external reference is not the problem you've asked for help with. You've reported that the device behaves as if it has a 5.0 volt reference whatever you configure the reference to be (correct me if I'm wrong). If you read my post of yesterday (Message #16793), you'll see that connecting the VREF pin to a voltage source and selecting an internal reference is probably a bad thing to do. Consult the data sheet for the device you're using. Now that you've done that, you won't be able to rely on the device working properly as some of the magic smoke has probably come out. In other words, you may have blown up the internal references and this could explain what you're now seeing.

Graham.





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