Ex_pulse using timer 1?

[jubilee]

hey all

i have problems using timer1 to time a pulse of aorund 10 to 11 HZ freq.

Questions is how long could timer 1 time?

isnt it: 65535 cycles before overflows
each cycle is : fosc/4
=20M/4 =5Mhz which is 200 n seconds


#include <16F872.h>
#fuses HS,NOWDT,NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) // Jumpers: 8 to 11, 7 to 12


void wait_for_low_to_high() {

while(input(PIN_B1)) ; /* if it's high, wait for a low */

delay_us(3); /* account for fall time */

while(!input(PIN_B1)); /* wait for signal to go high */
}

void wait_for_low() {

delay_us(3); /* account for rise time */

while(input(PIN_B1)); /* wait for signal to go high */
}
main() {


long time;
float newtime;

setup_timer_1(T1_INTERNAL); // Start timer 1
setup_counters( RTCC_INTERNAL, RTCC_DIV_256);

while (TRUE)
{
printf("\n\rWaiting...\n\r");

wait_for_low_to_high();
set_timer1(0);
wait_for_low();
wait_for_low_to_high();
time = get_timer1();
delay_ms(100);

newtime = time *0.0000512 ;

printf(" counter : %8lu\n\n\r", time);
// printf("period : %4x\n\n\r", newtime);
printf("time in us : %8f\n\n\r", newtime);
}
out put i get at hypoerterminal is rubbish , why?

[wedilo]

Hello,
you need an isr that should be called every 100ms or so?

No problem,
The timer will increment every 1.6us at 20MHz
An instruction (here one increment) need 4 machine cycles
So calculate: 20e6 / 4 / T1_DIV_BY_8 = 625000 increments a second
You need only 625000 / 10 = 62500 increments

So then initialize the timer1 as follows:

[jubilee]

try that timer 1 thing .

but varies it .. as in not using an interrupt to time 1 sec.
instead using timer1 to time a period .

[Ttelmah]