AVR-Chat

Dave,

I ramp the physical voltage into the port 0 up, and at about 5V, it hits the 1023 level.  So that's why I conclude it's referencing only the Avcc which I have tied to +5.

I have tried every combination of the Vref settings, one by one.   Including the 2.5V, the 1.1v internal, etc.  I get the same response (meaning full scale at 5v) in each case.

I have to believe that the chip does not that kind of significant bug - and I have also got to believe that the compiler works on this chip just as it's done on a couple of others.  

The most logical conclusion is that I am overlooking some footnote in a register explanation or something that is specific to this chip...

Regards,
JB


From: Dave McLaughlin 
Sent: Thursday, January 21, 2010 9:36 PM
To: AVR-Chat@yahoogroups.com 
Subject: RE: [AVR-Chat] Vref on ATTiny861a


  
Hi Jeff,

What results are you seeing from the ADC with this code?

What voltage have you got on Vref?

What else have you tried?

Dave.

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Jeff Blaine AC0C
Sent: 21 January 2010 17:47
To: AVR-Chat@yahoogroups.com
Subject: [AVR-Chat] Vref on ATTiny861a

I am having a tough time getting this chip to respond to any other ADC
voltage reference than the default AVcc.

The code snip is really simple... Below, using the MakroC Pro compiler,
however the results seem to be the same if I do the same using ASM
instructions instead of their bit-level defines.

I must be overlooking something. It seems so simple, driving me nuts that
it's not working right. I have used the same compiler and basic code to get
a mega328 to work. 

Appreciate any suggestions the group may have.

Thanks/jeff

REFS0_bit = 1; // 001 invokes external Vref as ADC reference
ADEN_bit = 1; // enable adc
ADSC_bit = 1; // start conversion
while(adsc_bit);
lb=ADCL; // get lower byte
ub=ADCH; // get upper byte
adc_rd0 = (256*ub) + lb; // build number

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