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PIC16F77A - ADC resolution

 
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Minh Lam



Joined: 06 May 2025
Posts: 1

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PIC16F77A - ADC resolution
PostPosted: Tue May 06, 2025 9:57 pm     Reply with quote
I'm working on the ADC module of PIC16F877A. The schematic is very simple, including a voltage divider connected to RA0: https://uomustansiriyah.edu.iq/media/lectures/5/5_2020_06_14!01_18_34_AM.pdf

What I do not understand is the resolution of the module. The ADC module has 10-bit resolution as read in the datasheet. I was guided that I should put #device ADC = 10 in the code. The real value would be read_adc() * 5/1023 . Everything is fine. My code is as follows:

Code:

#include <16f877a.h>
#include <def_877a.h>
#DEVICE ADC=10 //return 10 bit
#fuses HS, NOWDT, NOPROTECT, NOLVP, NODEBUG, NOBROWNOUT, NOCPD, NOWRT
#use delay(clock=8MHz)

#define LCD_RS_PIN PIN_A2
#define LCD_RW_PIN PIN_A3
#define LCD_ENABLE_PIN PIN_A5
#define LCD_DATA4 PIN_D4
#define LCD_DATA5 PIN_D5
#define LCD_DATA6 PIN_D6
#define LCD_DATA7 PIN_D7
#define LCD_DATA0 PIN_D0
#define LCD_DATA1 PIN_D1
#define LCD_DATA2 PIN_D2
#define LCD_DATA3 PIN_D3

#include <lcd.c>

float voltage;

void main() {
    setup_adc_ports(AN0);
    setup_adc(ADC_CLOCK_DIV_2);
    lcd_init();

    while(true) {
        set_adc_channel(0);
        delay_us(10); 
        voltage = (read_adc()*5.0)/1023;

        lcd_gotoxy(1, 1);
        lcd_putc("DHCN");   
        lcd_gotoxy(1, 2);
        printf(lcd_putc, "%1.2fV", voltage);
    }
}

But when I do not put the directive #device ADC = 10, the voltage must be divided by 65535 to get the correct voltage. OR, I can use ADC = 16 instead (?).

I'd highly appreciate it if someone can explain this. Thank you very much.
temtronic



Joined: 01 Jul 2010
Posts: 9475
Location: Greensville,Ontario

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PostPosted: Wed May 07, 2025 5:28 am     Reply with quote
pretty sure it's the printf format.

"%1.2fV"

to me 1.2 is bad, '1' is total number of digits, '2' is number of digits after decimal point

try '4.2' and see what happens.

The manual isn't very clear about this,2 or 3 more example would be nice.
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