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width of pulse

 
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elec.eng
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width of pulse
PostPosted: Wed Mar 19, 2008 11:15 am     Reply with quote
hi all;
i am using pic 16f877 with 20 MHz crystal ; i want to enter pulses from generator. i want to calculate the width of the pulse. my program give me reading to 10Khz, i face problem to read frequencies higher than 10K.
if any one has code plz tell me
lot of thanx
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed Mar 19, 2008 1:41 pm     Reply with quote
Quote:
I want to calculate the width of the pulse.

See this CCS example file:
Quote:
c:\program files\picc\examples\ex_ccpmp.c
elec.eng
Guest
PostPosted: Wed Mar 19, 2008 10:02 pm     Reply with quote
thanx for ur help but i use this code with my pic , and i still face the same problem , the basic cct for the pic 16f877 \ 20mhz such as for 16f877\ 4mhz instead i use 5pf at the 20mhz crystal
gjs_rsdi



Joined: 06 Feb 2006
Posts: 468
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pulses
PostPosted: Sun Mar 23, 2008 8:44 am     Reply with quote
if your capacitors 5pf change to 15 or 22
see bellow examples. ccp will latch timer1 when interrupt
best regards
joseph
Code:
//example1
//for consecutive frequency measurements
int frequencytime=0;
short int frequencycalcflag=0;
enable_interrupts(INT_CCP1);

void frequency_calculating ()
{
   if (frequencycalcflag==1)
   {
//      "calculating the frequency"
      frequencycalcflag=0;
   }
}

#int_CCP1
void CCP1_isr()
{   
   set_timer1(0);
   frequencytime=CCP_1;
   frequencycalcflag=1;   
}
//example2
//if the time for calculations (in pc) is too short, use as bellow
int frequencytime=0;
short int startflag=0;
//when you want to measure frequency start by enabling int.ccp1
enable_interrupts(INT_CCP1);

#int_CCP1
void CCP1_isr()
{   
   set_timer1(0);
   if (startflag==1)
   {
      frequencytime=CCP_1;
      disable_interrupts(INT_CCP1);
//    "calculating the frequency"
      startflag=0;//for the next time frequency check
   else
   {
      startflag=1;
   }   
}
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