[Tinyos-help] ADC sampling - ref voltage 2.5V, goes only upto 1.25V

[Amit Pendharkar]

Hi Guys,

I use motiev telosb board and am using adc to sample external signal on
adc0.

I am configuring the adc so that it uses Vref=2.5V using parameters
REFERENCE_VREFplus_AVss & REFVOLT_LEVEL_2_5.

But what I observe is that ADC mis-samples values above 1.25V and the
sampled values touch 0xFFF when i/p is 1.25V. Isnt it supposed to sample
till i/p is 2.5V???

For i/p  > 1.25V, sampled values are always 0xFFF !!!! Why so?

Clearly I cannot sample negative values since ADC is supposed to sample only
positive inputs, then why Vref=2.5 doesnt allow me to sample upto 2.5V?

Similarly ADC gives FFF for i/p = 0.75V and when configured with
REFERENCE_VREFplus_AVss & REFVOLT_LEVEL_1_5

On telosb board AVss, VeREF+ & Vref-/VeREF- pins are all connected to
ground, aren't they?

Can somebody please throw light on this

Thanks & Regards,
Amit Pendharkar
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