ADC data.. Is something fishy?
How is your ADC input connected to ground? The 80mV may come from the noise of the preceding components. If the ADC is connected directly to ground, you shouldn't get this high readings. (But even then not necessarily all zeros either. An occasional 1 or 2 is possible.)  


Check if your power is decently decoupled: caps 100nF close to the power pins.  
Check if the ADC's reference voltage is decently decoupled. Don't just connect to \$V_{DD}\$, but decouple via an RC filter, or, even better an LC filter.  
Make sure you have a solid ground: preferably a ground plane, in any case short and wide traces.  
Keep the ADC input's trace short, and low impedance. A high impedance trace will work as an antenna, and pick up all kinds of noise. (Probably not much of a problem: ADCs usually have a low impedance input). Don't use a looping test lead to connect the ADC input to ground.  


If you're sure you paid attention to these points the reading should never be 80mV. Could you post a picture of the board?