Timer 0 trouble

[khansaab]

Hello guys. A simple routine to utilize interrupt of timer 0 every 444 uSec isnt working. Following is the code. Could anyone plz help with trouble shooting it as after hours of wasting time on it I couldnt find fault.

Crystal = 4.194304 Mhz

void interrupt()
{
INTCON.T0IF = 0;
TMR0 = 227;
PORTA.F0 = ~PORTA.F0;
}

void main()
{
TRISA.F0 = 0; // Port A is output
TMR0 = 227;
INTCON = 0xA0;
OPTION_REG = 0x03; //Using prescaler of 16
for(;;
}

 

[Mr RB]

There are so many things wrong with your method.
1. you are just writing to TMR0, not adding or subtract so you get a latency error
2. writing to TMR0 causes a 2 inst latency as well
3. you cant use a prescaler on TMR0 if you are going to write to it

I just put some code up on the forum that will do what you need, see this page;
https://www.electro-tech-online.com/threads/zezj-zero-error-zero-jitter-period-algorithm.100299/

I think all you need to do is put the value 444 in PERIOD at the top of the code to make a interrupt of 444 TMR0 ticks, if you want 444 actual uS you need to use a corrected value 444 * 4194304/4000000 = 465.