ccp Questions

[ferrarilib]

i am doing rpm counter and i am using cpp metode

#INT_CCP1
ccp1_isr()
{

Value=CCP_1-oldValue;
oldValue=CCP_1;
gotCCP1 = TRUE;
}

void main()
{

float freq;
char i;
Value=0;
oldValue=0;
gotCCP1 = TRUE;

setup_ccp1(CCP_CAPTURE_RE); // CCP1 - rising edge
setup_timer_1(T1_INTERNAL|T1_DIV_BY_1);// Timer1 interrupt
enable_interrupts(INT_CCP1);
enable_interrupts(GLOBAL);

set_tris_C(0xAF); // All inputs except C4 and C6

while(TRUE) { // Start main program loop (endless)

while(!gotCCP1) // when is false stop and return 0.
{
Value=0;


}

freq=1.0/((float)Value*2e-6);
printf("Freq%f\r\n",freq);

gotCCP1 = FALSE;

}// while
}


but when i dont input signal the the output insn' t 0 but sametime the frequency sametime 0 !
there is sameone that can help me ?
how i can know when cpp interput is not used ?
thanks

[Haplo]

How is the variable 'value' defined? If the timer overflows between two rising edges (which it will), the line 'Value=CCP_1-oldValue;' may result in an incorrect value.

[asmallri]

You have forgotten to clear the CCP1 interrupt before you enabled it. The interrup flag may already be set which means you will have an interrupt event occur immediately the interrupt is enabled. In this case the first reading is rubbish..

Also you are fighting your own interrupt handler with value being set in the mainline and in the interrupt handler. This is why you are getting silly values. I suspect what you meant to do was:

[ferrarilib]

int16 Value,oldValue ;

but i don't undestand .

can you do example how works ?
thanks

[ferrarilib]

the problem is that when i dont have more interrupt the count stop

i have thy this too

while(TRUE) { // Start main program loop (endless)




disable_interrupts(INT_CCP1);
freq=1.0/((float)Value*2e-6);
gotCCP1 = FALSE;

enable_interrupts(INT_CCP1);
printf("Freq%f\r\n",freq);

}

but when the frequency is 0 reurrn always the last valure

[Ttelmah]

I'd say the key problem is here:

[ferrarilib]

[asmallri]

Do this and tell us the results

[Ttelmah]

I think I'd clear gotCCP, before re-anabling the interrupt. This woul allow it to again 'log' an edge that occured during the print time.

Best Wishes

[ferrarilib]

[asmallri]

[asmallri]

If you are going to use interrupts then you MUST leave the enable and disable statements in place. Interrupts WILL corrupt the results, maybe not now, maybe not tomorrow, but it is as sure as night follows day.

[ferrarilib]

[Ttelmah]

What is the likely range of input frequencies involved?.
Remember that Timer1, is only a 16bit counter, so the maximum interval between clock edges that can be handled by the approach you are using here, corresponds to just over 30Hz (at 8MHz). If your frequency drops below this, you really need to add a timer1 interrupt, and increment a 'carry' bit, and use 32bit values for the count.
Conversely, if the frequency is relatively high, there will be significant 'jitter' in the measurement. If (for example), the time is about 0.1mSec/cycle, unless the clock is synchronous to the internal processor clock, values will jump between perhaps 199,and 201 counts, and the frequency measure will show about 1% fluctuation, even if the clock is perfectly stable.
Something seems to be 'screwy' about your maths.
As shown, a frequency of 10000Hz, will give counts around 200, and should be converted, by using:
freq=2E6/Value;
For the same count value, your conversion would give:
1/(200*2E-6) = 2500...
The single division will also need less maths time.

Best Wishes

[ferrarilib]

thanks now i undastand and my project start go on ..
yes i have implement with timer1 (#INT_TIMER1) so i have carry bite. and i have used union variable for do it to 32 bit.



I have resolve the problem whitout delay but with

if(period>2000000)
{
period=0;

}
in the CCP1 function (interrupts) so dont give to me error

and all is good now. So when the cicle is down 2000000 (1hz) the counter give to me 0.