you dont need to set adcon0 register if you are using picbasic.

Use Adc defines ;

Code:
DEFINE ADC_BITS  10      ' ADCIN resolution  (Bits)
    DEFINE ADC_CLOCK 3      ' ADC clock source  (Fosc/8)
    DEFINE ADC_SAMPLEUS 50 ' ADC sampling time (uSec)
YOU HAVE TO SET ADCON1 REGISTER TO CHOICE WITCH PORT ANOLOG OR DIGITAL.

Code:
       
ADCON1.7 = 1 ; Right justified.

ADCON1.3 = 1 ; PORTA.0 - ANALOG , AN2 - VREF(-) , AN3 - VREF(+)
ADCON1.2 = 1
ADCON1.1 = 1
ADCON1.0 = 1

MAIN :

ADCIN 0 , ADVAL

PAUSE 10
GOTO MAIN