Hi
I am using the 8dollars Upsd3434ev evaluation board by ST
Microelectronics for studying about the USB.
The datasheet is here

http://www.st.com/stonline/.../10976.pdf
I have learnt the USB interfacing and firmware and basic programs are working.Now have I started to work on the 10bit ADC on the chip for making a simple data aquistion system .This is were the problem starts.

1)When the inbuilt ADC is enabled and conversion is done with microcontroller with all peripherals ON the aquired readings are varying a lot about 4 bits.

2)When the ADC is enabled and conversion done with microcontroller in idle mode and all peripherals OFF the aquired reading does not vary at all.

The signal i am aquiring is from a 9v DC battery with all care to make signal noiseless.

I have seen the circuit diagram of the board and the ADC uses the Vref from the AVCC on the chip which is around 3.3V which it gets from on board regulator.

So Is this the problem of the chip or a hardware problem or i am not setting some registers right??
Since i have seen of people having worked on the same evaluation board can anybody guide me on this subject

Regards
Gopalakrishnan.Narayanan