(1)  Select analogue input. In our example, we chosed pin 11 of the chip,    
      which is AN2.
        
                               ANSEL=  0b00000100;

(2) Set CHS bits in ADCON0 to select the channel to connect to sample and  
     hold circuit. 
                  
                               ADCON0 <4:2>  =    _ _ _  0 1 0 _ _

(3) Set voltage reference source in ADCON0<6>.  0= VDD, 1= Vref pin. We 
     choose VDD as reference. So,

                                ADCON0 <6> =    _ 0 _ _ _ _ _ _ 

(4) Initiate ADC module by setting "1" in  ADCON0 <0>  ( doesn't mean A/D 
     conversion starts).
     Set DO/DONE bit in ADCON0<1> to off, not starting conversion yet. 
     ADCON0<1>= 0.   So,

                                ADCON0<1:0> =  _ _ _ _ _ _ 0 1

(5) Set A/D conversion format, left or right justified, in ADCON0<7>. The 
     result of the conversion is in 10 bits and will be stored in  ADRESH and 
    ADRESL register.  Left justified is :  xxxxxxxx   xx000000
                                          ADRESH      ADRESL
                                  
                            Right justified is: 000000xx   xxxxxxxx
                                                 ADRESH      ADRESL
    We choose left justified, so
      
                                ADCON0 <7> =  0 _ _ _ _ _ _ _

    To sum up for ADCON0:

                                ADCON0= 0b00001001; 

  
The setting with reference to the block diagram is complete.
When we want to start the conversion, we simply set GO/DONE bit to 1, ie 

(6)                             GODONE= 1;

 Next we have to set the conversion clock:

(7) Set the A/D conversion clock  (TAD)  in ADCON1 <6:4>.
     We have to ensure a mimimum of 1.6 uS TAD for proper A/D  operation.  
     For 4 MHz device frequency, we should select 8 Tosc (2.0 uS, which is >  
     minimum  requirement).  ADCON1 <6:4> =  001.   

                                 ADCON1= 00010000;  
      
     If we don't want to calulate this value, we can just set ADCON1 <6:4> to 
     x11. The TAD is 4 uS with this setting. 


To sum it all up, we only need three C statments to set up the ADC. 
Analogue input= AN2
Voltage reference source= VDD
Device OSC= 4MHz

C statments:
                 
                 
                     ANSEL=  0b00000100;
                     ADCON0= 0b00001001; 
                     ADCON1= 00010000;