> I am to use a 24FJxxGA106 to (along other things) measure 220V mains
> voltage with some coarse accuracy, say 1-2%

Is there a specific reason to use this chip?

My reason for asking is that Microchip have some application notes on using 
members of the dsPic family in a UPS, and you may be able to leverage code 
from that for your purpose. 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist