adding offset using PIC

[doryme]

Hello

I need to add offset to my AC signals entering to adc of pic16f877A.
I should check the most -ve value of the analog signal then add it as offset.
For example if the signal varies from 2.5 to -2.5 so my program should add 2.5 to the signal before it enters to adc.

Another question, what is the range of adc in pic16f877A?
And if my signal is more than this range how can I minimize it?!

Thanks

[SherpaDoug]

I am not intimately familiar with the 16F877A, but every PIC I have worked with has a max ADC range of 0V to VCC. So if you have an AC input that goes below GND you will have to either do an analog offset before the signal gets to the ADC, or or run the PIC 0V supply rail below ground.

The best bet is to read the datasheet for your PIC.
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[PCM programmer]

See this thread for techniques to shift the voltage level of analog input
signals to the PIC:
http://www.ccsinfo.com/forum/viewtopic.php?t=25005