I want to control the ADC Vref. How do I go about that? The Atmel data
sheet refers to a register that can be changed that does this but I do not
understand how to change that register and if I change it once will that
change presist through later restarts.
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From: Dave Hylands <dhylands@gm...> - 2006-04-24 14:09:17
On 4/23/06, Jonathan Stewart <aggie.stewart@...> wrote:
> I want to control the ADC Vref. How do I go about that? The Atmel data
> sheet refers to a register that can be changed that does this but I do no=
> understand how to change that register and if I change it once will that
> change presist through later restarts.
Figure 108 (on page 232) of the datasheet shows what's required.
Unfortunately, in order to be able to switch the ADC reference, the
AREF pin needs to be unconnected. On the robostix its currently
connected to AVcc.
If you lift pin 62 (the trace connecting 62 to 64 is under the
ATMega128 chip - so the only way to disconnect 62 is to lift the pin),
then you can use the REFS0 and REFS1 bits in the ADMUX register to
This register (and in fact all of the registers) will get reset to
their default value upon reset.
The only choices that you have (using the switch) are to use AVcc or
2.56v and these choices would only be available if the AREF pin is
Why are you trying to change AREF?
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