problem with mcs-51 to make voltmeter

Hello
I've a problem.

I want to make Voltmeter with mcs-51.So i decide to use a/d such as
adc0801 or adc0804 or adc0832,which of these is the best a/d chip to
suitable for making Voltmeter with mcs-51 and i also don't know how to
write assembly code for read input from a/d chip,please advice me please
(if you can send me some code or flowchart how to do this,i'll special
thanks)