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sleep() function problem with 18f2520

 
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nehallove



Joined: 16 Jan 2008
Posts: 61

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sleep() function problem with 18f2520
PostPosted: Wed Jan 30, 2008 2:52 pm     Reply with quote

Hi guys,

I am working on the project in which i have to wake up the unit from sleep mode after detecting the comparator output of the 18f2520's port pin.

Problems which i face are ...
1. comparator interrupt works pretty good without putting sleep function in. but whenever i put sleep function comparator interrupt fires even if there isn't possible condition to fire it up. and unit comes out of sleep.

2. if i remove sleep function then it works great. so is it debugger which messing it up or something else.

Code:
setup_comparator(A0_A3_NC_NC_OUT_ON_A4); // a0 & a3 comparator
setup_vref(FALSE); // input and a4 is output


enable_interrupts(INT_COMP); // Initialize the Comparator interrupt
enable_interrupts(GLOBAL); // Enable the requested interrupts

sleep();
while(1){
output_low(PIN_C2);
delay_ms(100);
output_high(PIN_C2);
}

#INT_COMP
void isr()
{
disable_interrupts(INT_COMP);
clear_interrupt(INT_COMP);
delay_ms(1000); // *** TEST CODE, wait to see if it works
output_high(PIN_C2); // *** TEST CODE, turn on LED
return;
}

regards:
_________________
nehal
Ttelmah
Guest







PostPosted: Wed Jan 30, 2008 3:31 pm     Reply with quote

_Clear_ the comparator interrupt before enabling it.
Remember it will already be set, if _any_ comparator event has already occured.
Unless you really 'need' to have the interrupt handler, get rid of it, and remove the 'global' interrupt enable. The interrupt will _wake_ the chip when it fires, even if the global enable is off, and execute the next instruction. So:
Code:

while (true) {
   clear_interrupt(INT_COMP);
   enable_interrupts(INT_COMP); // Initialize the Comparator interrupt
   sleep();
   delay_cycles(1); //The instruction after the sleep is 'prefetched'
   //This ensures it is a NOP
   output_low(PIN_C2);
   delay_ms(1000);
   output_high(PIN_C2);
}

With your comparator setups, this should sleep, and respond immediately (only a couple of instruction times delay), when the interrupt triggers, while the 'interrupt handler' approach, will add about 30 instruction times delay to this.

Best Wishes
Guest








PostPosted: Thu Jan 31, 2008 11:48 am     Reply with quote

hey thanks for the help.

i already did same way you showed me, but it didn't work. it doesn't go to sleep at all. it remains in constant loop. It responses to comparator interrupt but if i remove comparator interrupt then it doesn't have any problem going to sleep. Is any relationship between comparator interrupt and sleep mode???

nehal
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