How to measure pulse low period using CCP

[engr.waqas]

Hi
I'm using CCS C compiler's example file to measure pulse width( high time). I want to change this example program to measure pulse low time. Can you please help me how can I do that ?
Below the example file which measure high time.

long rise,fall,pulse_width;

#int_ccp2
void isr()
{
rise = CCP_1;
fall = CCP_2;

pulse_width = fall - rise; // CCP_1 is the time the pulse went high
} // CCP_2 is the time the pulse went low
// pulse_width/(clock/4) is the time

// In order for this to work the ISR
// overhead must be less than the
// low time. For this program the
// overhead is 45 instructions. The
// low time must then be at least
// 9 us.

void main()
{
printf("\n\rHigh time (sampled every second):\n\r");
setup_ccp1(CCP_CAPTURE_RE); // Configure CCP1 to capture rise
setup_ccp2(CCP_CAPTURE_FE); // Configure CCP2 to capture fall
setup_timer_1(T1_INTERNAL); // Start timer 1

enable_interrupts(INT_CCP2); // Setup interrupt on falling edge
enable_interrupts(GLOBAL);

while(TRUE) {
delay_ms(1000);
printf("\r%lu us ", pulse_width/5 );
}
}

 

[taroot]

Read the value in interrupt and also use,

setup_ccp1(CCP_CAPTURE_RE); // Configure CCP1 to capture rise
setup_ccp2(CCP_CAPTURE_FE); // Configure CCP2 to capture fal

l
in interrupt.

 

[engr.waqas]

Thanks for your reply.
I already solved the problem few mins ago
here is working code for other's help


#include <18F452.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)



long rise,fall,pulse_width;

#int_ccp1
void isr()
{
rise = CCP_1;
fall = CCP_2;

pulse_width = rise-fall; // CCP_1 is the time the pulse went high
} // CCP_2 is the time the pulse went low
// pulse_width/(clock/4) is the time

// In order for this to work the ISR
// overhead must be less than the
// low time. For this program the
// overhead is 45 instructions. The
// low time must then be at least
// 9 us.

void main()
{
printf("\n\rLow time (sampled every second):\n\r");

setup_ccp2(CCP_CAPTURE_FE); // Configure CCP2 to capture fall
setup_ccp1(CCP_CAPTURE_RE); // Configure CCP1 to capture rise
setup_timer_1(T1_INTERNAL); // Start timer 1

enable_interrupts(INT_CCP1); // Setup interrupt on rise edge
enable_interrupts(GLOBAL);

while(TRUE) {
delay_ms(1000);
printf("\r%lu us ", pulse_width/5 );
}
}

 

[Tahmid]

A hardware solution could be to invert the signal using a transistor or NOT gate and use the code (the first one). Since the signal is now inverted, you are actually reading the low time.
:smile: