PIC16F873 A/D conversion program

;The A/D test program for PIC16F873 implements the following functions:
;(1) Use RA0/AN0 as the A/D conversion input channel;
;(2) The reference voltage source VREF selects the internal VDD and VSS;
;(3) The A/D conversion clock source selects a 4MHz oscillator;
;(4) Eight-bit data accuracy, and the AD result is written to port C.

;8L8ADSY.ASM A/D conversion
list p=16f873
INCLUDE "P16F873.INC"

       ORG 0x000
MAIN
       NOP
       BANKSEL ADCON1 ;Select RAM data memory bank 1, equivalent to BSF STATUS, RP0
       MOVLW B'00000000' ;Select RA5/AN4 as analog input, the result format is left-aligned
       MOVWF ADCON1 ;Select internal VDD and VSS for reference voltage source VREF
       CLRF TRISC ;Set port C as output
       BANKSEL ADCON0 ;Select RAM data memory bank 0, equivalent to BCF STATUS, RP0
       MOVLW B'01100001' ;Set clock source 8Tosc, enable ADC, AN0 channel is selected
       MOVWF ADCON0
       CLRF PORTC ;Clear port C

AtoD
       NOP; In order to ensure the sampling time, usually,
       a NOP of more than 20us should be inserted; Time delay or arrange a considerable length of application.
       BSF ADCON0,GO; GO position 1, start A/D conversion
ADWAIT
       BTFSC ADCON0,GO; After the A/D conversion is completed, the GO bit will be cleared to 0
       GOTO ADWAIT; If the conversion is not completed, return to continue testing
       MOVF ADRESH,W; If the conversion is completed, read the A/D result into W
       MOVWF PORTC; Write the AD result to port C
       GOTO AtoD; Cycle A/D conversion
       END