...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.
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  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
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
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.+
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
__config _LVP_OFF & _RC_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF & _BODEN_ON & _DEBUG_OFF
Est equ 0x20
Nord equ 0x24
Ouest equ 0x26
;Set up for A/D convergion
; LIRE A/D CHANNEL 0 , OUEST
; clrf PORTC
; clrf Ouest
; clrf Est
; clrf Nord
; LIRE A/D CHANNEL 1 , Nord
; clrf PORTC
; clrf Ouest
; clrf Est
; clrf Nord
; LIRE A/D CHANNEL 2 , EST
; goto Main
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.ThnxJames Newton replies: See General Midi IO+
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