Hello all,

New to this forum and to pic programming.
I am working on a circuit using the 16F877A using the ccs-C compiler.
In this circuit I am required to send an input the timer0 of the PIC (by adjusting a variable resistor connected to 5V & Gnd) via pin #6 (RA4/T0CKI/C1OUT). The issue is that I do not know what function to use to read the input and act accordingly.
Can anyone suggest a (if not the) function I should use.

Thanks a lot in advance.

 

I think you are mistaken. You probably need to use the ADC not Timer0 to read the voltage on the variable resistor.

 

Well, the pin will register something if you throttle the variable resistor back and forth a whole lot, it could be used to count a whole lot of bunch of wiggling.

To really know what's going on, what's the purpose of this program?

 

This is what I intend to do with my circuit.
I want to use the variable resistor to control the frequency an LED blinks.
I'm copying a certain part of the code so that it will be easy to understand


#int_rtcc
void timer0_isr(void){
set_timer0(55);
clk_counter++;
rt_clock(); //User defined function
}

void rt_clock(void){ //Configures a 500ms flashing status LED
if(status_led==9)
{
status_led=0;
output_toggle(PIN_C0); //LED output toggled every 500ms
}
else{
status_led++;
}
}


This is what I want to do. Instead of "set_timer0(55)" I want it to be "set_timer(x)" where 'x' is a variable that will change when the variable resistor is adjusted.
The variable resistor is connected to pin #6 (which is RA4/T0CKI/C1OUT according to the data sheet) - and the 2 ends of the variable resistor are at 0 & 5 V respectively.
And then again the data sheet says that pin #6 (T0CKI) is the timer0 input so I presumed that the PIC would directly read it without having to use an ADC.

So now my Q is - How do I use an ADC to read off the resistor and transfer it to 'x'?

 

I just flipped through the 16f877A data sheet, and you picked the ONE pin in the dead center of eight A/D converters that isn't one. On the data sheet the "an(x)" pins are the A/D converters.

To run the ADC, you need to set a bit in the "ADC0N" register (I just closed the data sheet- i'm not looking up the register address) to initialize the ADC, then it takes a few clock cycles, after that a bit in ADC0N will go high as a 'converstion finished' flag. Then you can read the results right off the ADRES register.

Make sure you define some of the bits in the ADC0N register properly- they've given me issues in the past (the past two weeks- oh ho!)


On the electronics side, you'll need a pot or a voltage drop- just adjusting the resistance off of a power rail won't play with the voltage.


I know that i've omitted a lot of information in this answer- i'm still learning a bit myself. The way I see it, a little bit more than what you have is often just enough to point you in the right direction.

Best of luck!