[SOLVED] PIC complete discussion for all

vinodstanur · Jun 16, 2011

yes............

romel_emperado · Jun 16, 2011

the calcultor you have given is not working.. I mean the plugin is not working

I have this calculator but it seems it's not possible to generate directly a 250ms..

PIC Timer Calculator

vinodstanur · Jun 16, 2011

You can use timer interrupt and in ISR you can increment some variable.

romel_emperado · Jun 16, 2011

vinodstanur said:
You can use timer interrupt and in ISR you can increment some variable.

yes. but look at this.. I got this in the calculator 0.00204800sec @4Mhz. it is very small time.. hard to get a fixed delay..

vinodstanur · Jun 16, 2011

PIC16F877 Timer Modules tutorials | PIC timer0 tutorial

romel_emperado · Jun 16, 2011

vinodstanur said:
PIC16F877 Timer Modules tutorials | PIC timer0 tutorial

when count reachest to 15 reset to 0.. but why 15? how would this program produce 1 sec delay?? i dont get it.

ckshivaram · Jun 16, 2011

this answers your question
**broken link removed**
**broken link removed**

romel_emperado · Jun 16, 2011

Hi guys... sorry for causing you trouble here... :grin: hehe.. I will attend my class first then I will back here and I will surely post the answer of my problem..

ckshivaram · Jun 17, 2011

hi romel,

I understand your anxiety.. but i feel this is the simplest tutorials you would get.
have a look at it.. this has clear explanation of everything.

PIC16F877 Timer Modules tutorials | PIC timer0 tutorial

romel_emperado · Jun 17, 2011

thanks. .. I have that link and I will read that today.. time here now is 1pm and I'll be out in school at 5pm then I will read that.. I will not sleep if I cant produce a 1 sec delay... hihihi

romel_emperado · Jun 17, 2011

Hi . just want to be sure..

fclk is clock frquency. right? it is not mentioned in the tut..

ckshivaram · Jun 17, 2011

yes sir you are right......

romel_emperado · Jun 17, 2011

hi.. I understand now the internal clock how to generate a delay of 0.5sec but I need clarification on the external clock based on the tutorial..

In PIC16 and 18F families 1 instruction cycle = 4 crystal cycles

but why in the formula of external clock 4 crystal cycles in not used? I mean it is not use as part of the divisor.(see the formula below.)

Formula to calculate Cout using Timer0

In this case there is no division by 4 of the original clock. We use the external frequency as it is.
If using EXTERNAL clock source (oscillator), the division is performed as follow:

ckshivaram · Jun 17, 2011

for external clock the divisor of 4 is default value, but in software you need to specify the clock used and activate the divisible by 4.

ckshivaram · Jun 17, 2011

check this thread
it has mazidi book on pic.. these books are bible for PIC and same in case of 8051
https://www.edaboard.com/threads/199392/#post840997 post 8

romel_emperado · Jun 17, 2011

hi..

what's the problem with this code? I followed the instruction in many tutorial but why the timer0 interrupt is still not working?

I can generate 1 second delay using timer0 without using interrupt and it's working fine but when i use timer interrupt it's not working anymore..

PHP:

#include<pic.h>

__CONFIG(0x3F38); //for Internal oscillator

void interrupt timer0()
{
	char count;
	if(T0IF == 1) 
	{
	    T0IF = 0;  //reset flag
	    count++;  // increment counter
		if(count == 15) // set timer to count 15 aprox to 1 second delay.
		{
			RA2 ^= 1;   //toggle LED
			count = 0;  //reset counter
		}
	}
}


void main(void)
{

	TMR0 = 0;
	OPTION_REG = 0b0111;  // set prescaler to timer 0 and 1:256 prescaler..
	T0CS = 0;  // timer 0 Internal clock source
	T0IE = 1;  // enable timer 0 interrrupt
	GIE =1;    // Enable global interrupt 
	TRISA2 = 0; //set bit 1 of portB as output.

	while(1);

}

ckshivaram · Jun 17, 2011

where do you disable the interrupt before exiting the ISR routine??

vinodstanur · Jun 17, 2011

Peie=1; ........

romel_emperado · Jun 17, 2011

wahahahaha Im happy now!!! I got it !!!

I just read the lines from a book and found out my mistake!!! :-D

**broken link removed**

my mistake is I declared a variable inside the interrupt function... that single line cost me almost 2 days of finding out why interrupt is not working... hehehe.. I can proceed now to next topic... hehe

---------- Post added at 13:28 ---------- Previous post was at 13:21 ----------

ckshivaram said:
where do you disable the interrupt before exiting the ISR routine??

I dont have that function yet.. though the program is working.. is it required? what is the effect if I dont have that?

anyway here is my working code now...

PHP:

#include<pic.h>

__CONFIG(0x3F38); //for Internal oscillator

char count;

void interrupt timer0()
{
	
    
	if(T0IF == 1)
	{
	    T0IF = 0;
//		PEIE = 0;
	    count++;
		if(count == 15)
		{
			RA2 ^= 1;  //toggle LED
			count = 0;
			
		}
	//	PEIE = 1;
	}
}


void main(void)
{

	TMR0 = 0;
	OPTION_REG = 0b0111;  // set prescaler to timer 0 and 1:256 prescaler..
	T0CS = 0;  // timer 0 Internal clock source
	T0IE = 1;  // enable timer 0 interrrupt
	GIE =1;    // Enable global interrupt 
	TRISA2 = 0; //set bit 1 of portB as output.

	while(1);

}

---------- Post added at 13:44 ---------- Previous post was at 13:28 ----------

vinodstanur said:
Peie=1; ........

thanks vinodstanur,

the last code i have posted above is still working without disabling or enabling peripheral bit.. and if I add that it is still working..
any cons if i dont have that? what's the difference of having or without it?

ckshivaram · Jun 17, 2011

its a good programming practice to use these bits and disable the interrupt routine before exiting... they are basic rules as they are of very much concern when your program runs on the real hardware and you wish to use more interrupts, then if interrupt is not disabled it will not allow other interrupts to execute due to its priority and other factors...

it works on simulator ,but real time application on real hardware, should also should be kept in mind.....

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