i use this code but is not working

Code:
DEFINE ADC_BITS 10
DEFINE ADC_SAMPLEUS 50
'DEFINE ADC_CLOCK 3

ADCON0  = %00000001
ADCON1  = %01100011
ANSELA = %00000111
TRISA   = %00000111
How to enable three channels (AN0,AN1,AN2) A/D converter PIC16F1827
any help please