Datasheet

PIC18F2XK20/4XK20
DS41303G-page 270  2010 Microchip Technology Inc.
19.2.9 A/D CONVERSION PROCEDURE
This is an example procedure for using the ADC to
perform an Analog-to-Digital conversion:
1. Configure Port:
• Disable pin output driver (See TRIS register)
• Configure pin as analog
2. Configure the ADC module:
• Select ADC conversion clock
• Configure voltage reference
• Select ADC input channel
• Select result format
• Select acquisition delay
• Turn on ADC module
3. Configure ADC interrupt (optional):
• Clear ADC interrupt flag
• Enable ADC interrupt
• Enable peripheral interrupt
• Enable global interrupt
(1)
4. Wait the required acquisition time
(2)
.
5. Start conversion by setting the GO/DONE bit.
6. Wait for ADC conversion to complete by one of
the following:
• Polling the GO/DONE
bit
• Waiting for the ADC interrupt (interrupts
enabled)
7. Read ADC Result
8. Clear the ADC interrupt flag (required if interrupt
is enabled).
EXAMPLE 19-1: A/D CONVERSION
Note 1: The global interrupt can be disabled if the
user is attempting to wake-up from Sleep
and resume in-line code execution.
2: Software delay required if ACQT bits are
set to zero delay. See Section 19.3 “A/D
Acquisition Requirements”.
;This code block configures the ADC
;for polling, Vdd and Vss as reference, Frc
clock and AN0 input.
;
;Conversion start & polling for completion
; are included.
;
MOVLW B’10101111’ ;right justify, Frc,
MOVWF ADCON2 ; & 12 TAD ACQ time
MOVLW B’00000000’ ;ADC ref = Vdd,Vss
MOVWF ADCON1 ;
BSF TRISA,0 ;Set RA0 to input
BSF ANSEL,0 ;Set RA0 to analog
MOVLW B’00000001’ ;AN0, ADC on
MOVWF ADCON0 ;
BSF ADCON0,GO ;Start conversion
ADCPoll:
BTFSC ADCON0,GO ;Is conversion done?
BRA ADCPoll ;No, test again
; Result is complete - store 2 MSbits in
; RESULTHI and 8 LSbits in RESULTLO
MOVFF ADRESH,RESULTHI
MOVFF ADRESL,RESULTLO