floating value of ADC pic16f877

[mamech]

Hello

I tried to read from analog pin and read it on my computer using terminal program. I used the following code:

unsigned int temp_res;

void main() {
ADCON0 = 0x00;

TRISA = 0xFF;
TRISC = 0;
TRISB = 0;
UART1_Init(9600);
Delay_ms(100);
UART1_Write_Text("Start");
UART1_Write(10);
UART1_Write(13);


do {

temp_res = ADC_Read(2); // Get 10-bit results of AD conversion
if (UART1_Data_Ready()) { // If data is received,

UART1_Write(temp_res); // and send data via UART
}

PORTB = ~ Portb;
Delay_ms(2000);
} while(1);
}

So I am reading the value on the pin and send it by serial to computer. I change the value of the analog i/p using a pot.

But there are a problem facing me. The value that I read on terminal program swings and does not stabilize even if I disconnected the pot and connected the supply directly.

Why does this happen?

 

[andre_luis]

Just to check : What C compiler are you using ?

+++

 

[mamech]

I use MicroC

 

[andre_luis]

mamech

The structure of program seems be strictly apropriate.
However, we don´t know how the API ADC_Read were implemented in compiler.

Thus, I can sugest you research in that compiler if there exist a way to you monitor A/C SFR to check if conversion finish were achieved.


+++

 

[mamech]

Actually I do not know if what I am facing is normal or not. I attach a photo captured from my terminal program, while receiving fixed analog i/p value from potentiometer.



The value displayed is not stable even if there is no change.

Actually I do not think that the compiler is involved in this problem. I have some doubts:

1-The defined variable in microC is unsigned int, and it should be max 2^10 -1 value because the limitation of the ADC. The terminal program has only 2 suitable formats to show the :twisted:ed int 10 data?

2-What is the refere i/p value nce voltage that the ADC compare the with? Does it compares with VCC?

Thanks