Thanx mr.nomad,

It is very useful,i followed ur statement and did the followin,tell me is it correct?

movlw b'00000000' ; select PORTA,0
movwf ADCON0
movlw b'00000001' ;switch on ADC
movwf ADCON0
here btfss ADCON0,2 ;checking whether conversion is in process or not
goto here
movf ADRES,0
movwf volt_val