...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:
Questions:
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
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
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+
Comments:
.