16F877 A/D IO Sample Programs

...the ground pin next to the port A pins is used internally in a way that is much closer to the A/D converter, and is thus meant to be the analog ground.

JB says:

After trying unsucessfully to get Microchip's example code (among others) to work, I hacked out this modification which seems to do the job, at least for me. If anyone else is having as a much difficulty as I did, this may help get things going. FWIW, the remaining least-significant bits are in ADRESL but this example makes use of the most-significant 8 bits left justified into ADRESH.

;16f877 a/d test routine
;
;TEST CIRCUIT:
;pin 11 & 32 = 5VDC
;pin 12 & 31 = 0VDC
;pin 1 = 5VDC
;pin 2 = 0 - 5 VDC analog input (center tap on 20k variable resistor)
;pin 13 & 14 = 4MHz crystal with 18pF capacitors to 0VDC
;pin 15,16,17,18,23,24,25,26 PORTC outputs each to 330 ohm resistor
;       in series with LED to 0VDC
;**********************************************************

        __config _LVP_OFF & _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF & _BODEN_OFF
& _DEBUG_OFF
        list p=16f877

        include "p16f877.inc"

        ; Start at the reset vector
        org     0x000
        goto    Start
        org     0x004
Interrupt
        retfie
Start
        bsf     STATUS,RP0      ;bank 1
        bcf     STATUS,RP1
        movlw   H'00'
        movwf   TRISC           ;portc [7-0] outputs
        clrf    ADCON1          ;left justified, all inputs a/d
        bcf     STATUS,RP0      ;bank 0
        movlw   B'01000001'     ;Fosc/8 [7-6], A/D ch0 [5-3], a/d on [0]
        movwf   ADCON0
Main
        call    ad_portc
        goto    Main


ad_portc
                                ;wait for acquision time (20uS)
                                ;(non-critical for this test)

        bsf     ADCON0,GO       ;Start A/D conversion
Wait
        btfsc   ADCON0,GO       ;Wait for conversion to complete
        goto    Wait

        movf    ADRESH,W        ;Write A/D result to PORTC
        movwf   PORTC           ;LEDs
        return

        end

Mark Willcox modified Tony Nixons program

;pwm.asm to learn CCP/PWM of 16f873. Last edited 5/23/2000
;Originated by Tony Nixon and modified by Mark Willcox.
;Grahm
;   This code will light a LED on portC pin RC2/CCP1 and 
;display the 8 bit hex value on portB LEDs or bargraph. The CCP1 LED
;will glow from bright to dim as the pot varies the pulse width. 
;Connect an O-scope to CCP1 and watch the PW vary. This code can be 
;used on other PICs but you will have to change the code to fit it's 
;instruction set. One wire on pot goes to +Vdd and the other end 
;of the pot goes to -Vss/ground. The wiper goes to RA0 input pin.
;You can use any input signal source as long as you don't exceed the 
;chips max specs. For example, a slow sine or ramp wave(1-5Hz) will 
;flash the CCP1 LED. Make sure you use a common ground for the 
;signal generator and PIC board.


        #include <p16F873.inc>
        LIST p=16F873
	errorlevel 1,-302	;to disable MPLAB bank warnings.
        __config _XT_OSC & _PWRTE_ON & _WDT_OFF & _LVE_OFF
		;Some versions of MPLAB use _LVP_OFF
		;This sets all portB pins to output.
;/*---------Declare Registers
STATUS	EQU	03
ADCON	EQU	08
PORTB	EQU	06
F       EQU     1
W       EQU     0
;/*---------Set up chip parameters
	CLRF	CCP1CON	;CCP MODULE IS OFF
	CLRF	TMR2	;CLEAR TIMER2
	MOVLW	0X7F	;
	MOVWF	PR2
	CALL	A2D
	CLRF	INTCON		;DISABLE INTRPTS ANDCLEAR T0IF
	BSF	STATUS,RP0
	BCF	TRISC,2		;MAKE PIN 2 PWM OUTPUT
	CLRF	PIE1		;DISABLE PERIPHERAL INTS
	BCF	STATUS,RP0
	CLRF	PIR1		;CLR PER INT FLAGS
	MOVLW	0X2C		;PWM  MODE, 2LSBs OF DUTY CYCLE=10
	MOVWF	CCP1CON
	BSF	T2CON,TMR2ON	;TIME2 STRTS TO INCREMENT
	;
	 ;CCP1 INT IS DISABLED
	 ;DO POLLING ON THE TMR2 INT FLAG BIT
	;
PWM_PERIOD_MATCH
	BTFSS	PIR1,TMR2IF
	GOTO	PWM_PERIOD_MATCH
	;
	 ;UPDATE THIS PWM PERIOD AND THE FOLLOWING PWM DUTY CYCLE
	;
	BCF	PIR1,TMR2IF
A2D     bsf     STATUS,RP0
        MOVLW   B'00000001'
        MOVWF   TRISA           ;All outputs except RA0.
        CLRF    TRISB		;RA0 is wiper of 50k pot/Vin
        CLRF    TRISC		;PortB is 8 LED output to show 
        MOVLW   B'00001110'     ;Hex value of Vin from pot.
        MOVWF   ADCON1		;left justified, RA0 = input
;/*-----Set up A2D parameters
        MOVLW   B'11010111'     ;prescaler 1:256 tmr0, internal clock
        MOVWF   OPTION_REG
        BCF     STATUS,RP0
        MOVLW   B'01000001'     ;a2d = on, ch0, fosc/8
        MOVWF   ADCON0
;/*-----Delay loop to settle A2D, similar to de-bounce???
mnloop  btfss   INTCON,T0IF     ;50us loop delay @ 4Mhz
        goto    mnloop
;/*-----Stop timer0 interrupt
        BCF     INTCON,T0IF
        BSF     ADCON0,GO_DONE  ;start a2d conversion
WAITA2D NOP                     ;wait 4 finish
        BTFSC   ADCON0,GO_DONE
        GOTO    WAITA2D
;/*-----Put A2D/PWM value in W and send to ports.
        MOVF    ADRESH,W        ;upper 8 bits-ignor lower 3
        MOVWF	CCPR1L		;PWM is output on pin 13 of 16F873
        MOVWF   PORTB		;output Hex value to LEDs
        RETURN			;DUTY CYCLE IS 25% OF PWM PERIOD
        
   END     	

See:

• PWM@

Questions:

• @spam@chminhtri at yahoo.com asks:

  Hello to all, I am presently trying to program the PIC 16F876 to read in 2 analogue values on 2 different channels.But after the first reading , ADRESH:ADRESL registers continue to contain the value of the this conversion, so that result ofthe second reading is failed. How I can reset ADRES pair for futher reading ?
  Thank you for your time and patience.
  Tri Chau_Nha Trang City

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• sphiwe Bethuel Makgathole;a asks:

  I'm looking for a program and circuit diagram to build a digital voltmeter(ADC) using pic16f627/8 that can measure voltages from from 0 to 30 volts. Voltages measured have to displayed on 2 LED's.Any advice on digital voltmeters will be appreciated.

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• @spam@s22793 at rmc.ca asks:

  Hello to all, I am presently trying to program the PIC 16F876 to read in 3 analogue values on 3 different channels and saving these values to different registers, for some reason, I cannot seem to get the proper values. I am using the C port to display what is being read onto the led's so i can see. I was wondering if you might have time and would not mind taking a look at my code because i just can't get it. for testing purposes, I only call one of the routines in the main at a time because i know that it would execute way to fast for me to see anything on the leds.
  
  Thank you for your time and patience
  
  Tania Maurice
  ****************************************************
  __config _LVP_OFF & _RC_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF & _BODEN_ON & _DEBUG_OFF
  LIST p=16f876
  include "p16f876.inc"
  
  org 0x000
  goto Start
  org 0x004
  
  Est equ 0x20
  Nord equ 0x24
  Ouest equ 0x26
  Interrupt
  retfie
  ;Set up for A/D convergion
  Start
  bsf STATUS,RP0
  bcf STATUS,RP1
  movlw H'00'
  movwf TRISC
  movlw H'00'
  movwf TRISB
  clrf ADCON1
  bcf STATUS,RP0
  clrf ADCON0
  clrf PORTC
  clrf Ouest
  clrf Est
  clrf Nord
  clrf PORTB
  
  goto Main
  
  ; LIRE A/D CHANNEL 0 , OUEST
  
  
  ad_portcOuest
  ; clrf PORTC
  ; clrf Ouest
  ; clrf Est
  ; clrf Nord
  clrf ADRESH
  movlw B'10000001'
  movwf ADCON0
  
  testingOuest
  bsf ADCON0,GO
  
  WaitOuest
  
  btfsc ADCON0,GO
  goto WaitOuest
  
  movf ADRESH,W
  movwf Ouest
  clrw
  movf Ouest,W
  movwf PORTC
  clrf ADRESH
  return
  ; LIRE A/D CHANNEL 1 , Nord
  ad_portcNord
  
  
  
  ; clrf PORTC
  ; clrf Ouest
  ; clrf Est
  ; clrf Nord
  clrf ADRESH
  movlw B'10001001'
  movwf ADCON0
  testingNord
  bsf ADCON0,GO
  
  WaitNord
  
  btfsc ADCON0,GO
  goto WaitNord
  
  movf ADRESH,W
  movwf Nord
  clrw
  movf Nord,W
  movwf PORTC
  clrf ADRESH
  return
  ; LIRE A/D CHANNEL 2 , EST
  ad_portcEst
  clrf PORTC
  clrf Est
  movlw B'10010001'
  movwf ADCON0
  testingEst
  bsf ADCON0,GO
  
  WaitEst
  
  btfsc ADCON0,GO
  goto WaitEst
  
  movf ADRESH,W
  movwf Est
  clrw
  movf Est,W
  movwf PORTC
  clrf ADRESH
  return
  
  
  
  
  
  Main
  
  call ad_portcOuest
  call ad_portcNord
  call ad_portcEst
  
  
  ; goto Main
  
  
  
  
  
  end

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• @spam@drumster71 at hotmail.com asks:

  I am looking for a program to convert signal from peizo disks to midi drum code for the 16f877.Any other advice on the midi subject would be greatly appreciated.Thnx

  James Newton replies: See General Midi IO+

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Comments:

• @spam@ing_njospina at hotmail.com " thanks" +
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