Thank, but is good use only one command
not sure if i follow you. Could you explain it a little it more?

For the 877, there's no analog comparator, only the 877A will have it.

If you want to know the possible values , use my PicMultiCalc
http://www.mister-e.org/pages/utilitiespag.html

once done is just a matter to read a little bit the datasheet in the analog comparator section, register CMCON and CVRCON