ADC library must support negative ADC results

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The ADC library currently assumes that the result of an A-D Conversion is 
always a positive value (byte or word). However, the ADC modules of newer PICs, 
e.g. 16F1783, support negative results of ADC. With 12-bits resolution this 
means the result can be in the range -4096 to +4095.  A modification of the 
library is desired to support and return signed values.

Original issue reported on code.google.com by robhamerling on 17 Apr 2013 at 8:40

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Original comment by robhamerling on 17 Apr 2013 at 8:41

• Changed title: *ADC library must support negative ADC results *

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Currently I limit my tests and analysis to the 16f1783, but I expect that other 
14H PICs suffer of similar omissions the ADC libraries. Later other PICs - 
especially 14H - could be analyzed to obtain a complete picture of the required 
changes. I'll collect my findings here for the person(s) who will eventually 
update these libraries. 
The 16f1783 ADC module requires ADCON2 to be configured properly. As default 
'compatibility' setting it could be set to 0b0000_1111. See the datasheet for 
details.

Original comment by robhamerling on 17 Apr 2013 at 7:16