Help Me Pls,sampling!!!!!!!

Im having a problem in understanding how to set the sampling rate using the PIC16F887,i did read the data sheet own how to set the ADC and im still a bit confused.Basically what i need to do is to sample two sinusoidal signals which are at 50Hz (voltage and current).I want to sample this ac inpututs 20 times per 50Hz cycle.After each period(i.e 1/50Hz) i want to multipy the corresponding voltage and current to get the instantaneous power and display it on the onboard LEDs.This is the code i already have:

#include <p16F887.inc>
__CONFIG _CONFIG1, _LVP_OFF & _FCMEN_OFF & _IESO_OFF & _BOR_OFF & _CPD_OFF & _CP_OFF & _MCLRE_OFF & _PWRTE_ON & _WDT_OFF & _INTRC_OSC_NOCLKOUT
__CONFIG _CONFIG2, _WRT_OFF & _BOR21V

org 0x0

;------------- Voltage signal----------------------------

volts
movlw B'01000001' ;configure A/D converter
movwf ADCON0 ;turn A/D on
movlw b'10001110' ;RA0 = analog input
movwf ADCON1


volts_again
bsf ADCON0,GO ;start conversion
again
btfsc ADCON0,GO
goto again
movf ADRESH,W ;ADRESH --> WREG


;------------- Current signal--------------------------------------------

current
movlw B'01000001' ;configure A/D converter
movwf ADCON0 ;turn A/D on
movlw b'00001110' ;RA0 = analog input
movwf ADCON1

current_again
bsf ADCON0,GO ;start conversion
again1
btfsc ADCON0,GO
goto again1
movf ADRESH,W ;ADRESH --> WREG

please help me with the following

1.how can i implement taking 20 samples for each 50Hz cycle on the code
2.will the adc of the voltage and current occur simultaneously?if not how do i run the first adc of the voltage signal and there after run the second adc of the current signal,such that i will be able to multiply the corresponding digital votages and currents to get the correct intantaneous power

im using PIC16F887,your help will be appreciated

Hi, Hazda

First of all ... no need to "bomb" the forum with the same question. Once is enough.

second ... here we talk PicBasicPro, and not assembler ...


For what you should do, it's simple : just use a timer interrupt ( see "compare" feature of pics ... and add 1 ms to the value at each interrupt.) to initiate both conversions every 1 ms AND synchronize the timer reset with mains zero crossing.

Here is an example ( in MkBasic ! )

Code:

---


program Timer1ModeComparaison

' Pic 16F877 @ 8 Mhz

dim comparaison as word

sub procedure interrupt
    comparaison = comparaison + 500
    CCPR1L = comparaison          ' Ecriture poids faibles CCPR1L
    CCPR1H = word(comparaison >>8)' Ecriture poids forts CCPR1H
    PORTB = PORTB xor %00000001  ' Changement d'etat sortie Toggle output
    PIR1 = %00000000
    PIE1 = %00000100
    INTCON = %11000000
end sub

main:
    comparaison = 0
    TRISB = 0                      ' PORT B en sortie
    PORTB = 0
    T1CON = 1                      ' Validation timer 1 ; Timer1 ON
    CCP1CON = %00001010            ' Definition mode comparaison ; compare mode
    PIE1 = %00000100              ' Autorisation it comparaison      ; Compare interrupt enable
    INTCON = %11000000
    while true                    ' Boucle sans fin ; endless loop
    wend
end.

---

it outputs a 1 Khz signal on Portb.0 ... but ,instead, could initiate your conversions !!!

Alain