TMR0 interrupt

For C and ASSEMBLY users to post questions and code snippets for programming in C and ASSEMBLY. And for any other C or ASM course related questions.

Moderators: Benj, Mods

Post Reply
Posts: 3
Joined: Thu Jan 10, 2013 3:53 pm

TMR0 interrupt

Post by mircea2012 »

Hi all.

I am a beginner in Pic microcontroller. I bought a development board from Matrix Multimedia, HP488, but I don't know why I fail with a small program.

The program must flash a led with a delay (4 sec) using TMR0.
So, from my calculations, using formula :
Freq. out = Freq. osc / [prescaler * (256 - TMR0) * count]
The prescaler is 1 : 256; TMR0 is 0, anf the frequency oscilator is 4Mhz (osccon = 0b01100000)
An instruction is executed in 4 clock cycles. So the frequency clock is 4Mhz / 4 = 1Mhz.
count = 61.
I use sourceBoost IDE, and the compiler is BoostC.

Look my code :

unsigned int counter = 0;

void Delay(void)
if(intcon & 2) // check if TMR0IF is set
clear_bit( intcon, 2 ); // if TMR0IF is set, clear this bit
counter = counter + 1; // increments the counter
if(counter == 61)
counter = 0;
portb = ~portb; // flash the Led 0 of Port B

void main(void)
trisb = 0x00; // set all pins of Port B as output
portb = 0x01; // RB0 is high
tmr0 = 0; // the value of TMR0 register is zero.
cmcon = 0x07; // comparators is off.
option_reg = 0b00000111; // prescaler is assigned to the WDT, prescaler 1:256
intcon = 0b10100000; // GIE - enable, TMR0IE - enable
{ }
enter code here

The program compiles fine, upload fine, but dont show me the led flashing.
What I am doing wrong ? Are there any configuration settings that I am not aware of ?
(113.45 KiB) Downloaded 3225 times

Posts: 1314
Joined: Sun Jan 15, 2012 3:15 pm

Re: TMR0 interrupt

Post by dazz »


Im not very good with c or asm, but if you look at your config screens both internal and rc are ticked, if the oscalator is wrong it wont work

Best to start with switching on an led,if that works then switch it off, again if it works add your delays etc

To sign up to the V5 forum follow this link

User avatar
Valued Contributor
Valued Contributor
Posts: 8873
Joined: Sat May 05, 2007 2:27 pm
Location: Northamptonshire, UK

Re: TMR0 interrupt

Post by medelec35 »

Hi mircea2012,

If you would like to post your generated hex file, I can see if configuration settings are OK.
We can then take it from there.


If you read a post that is useful, please show appreciation by clicking on thumbs up Icon.

Post Reply