SUCCESSIVE APPROXIMATION ANALOGUE TO DIGITAL CONVERSION

Thu May 16, 2013 5:27 pm

Code:: ;SUCCESSIVE APPROXIMATION ADC TITLE "SAR ADC" list p =16f877 include <p16f877.inc> BANK0 macro bcf STATUS,RP0 bcf STATUS,RP1 endm BANK1 macro bsf STATUS,RP0 bcf STATUS,RP1 endm BANK2 macro bcf STATUS,RP0 bsf STATUS,RP1 endm BANK3 macro bsf STATUS,RP0 bsf STATUS,RP1 endm COUNTER EQU 0x20 RESULT EQU 0x21 MASK EQU 0x22 DELAY_TIME EQU 0x23 COMP EQU 4 TEMP EQU 0x24 ; ****** ORG 0 NOP GOTO START ;**** ; MAIN ROUTINE ORG 0x20 START CALL INIT ;INITIAbISE PORTS REPEAT MOVLW 8 ;COUNTER = 0 MOVWF COUNTER; MOVLW 0x80 ;SET MASK. MOVWF MASK; MOVWF RESULT ;SET INIT RESULT NEXT MOVF RESULT,W ;GET CJRRENT RESULT VALUE IORWF MASK,W ;SET NEXT MSB MOVWF PORTD ;AND OUTPUT CALL DELAY ;ALLOW TIME TO SETTLE BTFSS PORTA,COMP ;TEST COMP OUTPUT CALL SETBIT ;IF SET, CALL SETBIT BTFSC PORTA,COMP ;TEST COMP BIT CALL CLEARBIT ;ELSE CLEAR BIT BCF STATUS,C ;CLEAR CARRY FLAG RRF MASK ;SET NEXT MSB MOVLW 1 ;SET DECREb€NT SUBWF COUNTER ;AND DECREMENT BTFSS STATUS,Z ;TEST FOR LAST BIT GOTO NEXT ;AND DO NEXT BIT IF NOT GOTO REPEAT ;ELSE REPEAT ;**** SETBIT MOVWF RESULT RETURN ; CLEAR BIT CLEARBIT COMF MASK,W; GET CURRENT MASK AND INVERT ANDWF RESULT; AND CLEAR CURRENT BIT RETURN ; PORT INITIALISATION INIT BANK1 ; set to bank1 CLRF TRISD; SET PORT D TO OUTPUT MOVLW 06; MAKE PORT A DIGITAL MOVWF ADCON1 BSF TRISA,4 ; AND BIT A4 to INPUT BANK0; BACK TO BANK 0 RETURN ; DELAY ROUTIN DELAY MOVWF TEMP ; SAVE W MOVLW 0x80; set delay time MOVWF DELAY_TIME WAIT INCFSZ DELAY_TIME ; COUNT DOWN GOTO WAIT MOVF TEMP,W RETURN END