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Timer0 questions

 
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The Puma



Joined: 23 Apr 2004
Posts: 227
Location: The Netherlands

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Timer0 questions
PostPosted: Tue Oct 02, 2007 9:50 am     Reply with quote
i have this little programs thats blinks two leds.
How can i calculate om which freq the leds blinks?

Code:
#include <18F4620.h>
#use delay(clock=20000000)
#fuses HS,NOWDT,NOBROWNOUT,NOPUT,NOLVP,DEBUG,NOSTVREN,NOPROTECT

int8 GL1_counter,GL2_counter;

#define Green_Led_1      PIN_C1
#define Green_Led_2      PIN_C2

// LEDs blinking-time constants
#define Green_Led_1_blink  4
#define Green_Led_2_blink  8

#int_RTCC
void RTCC_isr() {
   GL1_counter--;
   if(!GL1_counter) {
      GL1_counter=Green_Led_1_blink;
      output_toggle(Green_Led_1);
   }
   GL2_counter--;
   if(!GL2_counter) {
      GL2_counter=Green_Led_2_blink;
      output_toggle(Green_Led_2);
   }
}

void main() {
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   GL1_counter=Green_Led_1_blink;
   GL2_counter=Green_Led_2_blink;
   enable_interrupts(INT_RTCC);
   enable_interrupts(GLOBAL);
   
   while(TRUE) {
      // ....
      // Your can do anything here while
      // your Leds are blinking in background
      // ....
   }
}
Neutone



Joined: 08 Sep 2003
Posts: 839
Location: Houston

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Re: Timer0 questions
PostPosted: Tue Oct 02, 2007 11:09 am     Reply with quote
The [spam] wrote:
i have this little programs thats blinks two leds.
How can i calculate om which freq the leds blinks?

Code:
#include <18F4620.h>
#use delay(clock=20000000)
#fuses HS,NOWDT,NOBROWNOUT,NOPUT,NOLVP,DEBUG,NOSTVREN,NOPROTECT

int8 GL1_counter,GL2_counter;

#define Green_Led_1      PIN_C1
#define Green_Led_2      PIN_C2

// LEDs blinking-time constants
#define Green_Led_1_blink  4
#define Green_Led_2_blink  8

#int_RTCC
void RTCC_isr() {
   GL1_counter--;
   if(!GL1_counter) {
      GL1_counter=Green_Led_1_blink;
      output_toggle(Green_Led_1);
   }
   GL2_counter--;
   if(!GL2_counter) {
      GL2_counter=Green_Led_2_blink;
      output_toggle(Green_Led_2);
   }
}

void main() {
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
   GL1_counter=Green_Led_1_blink;
   GL2_counter=Green_Led_2_blink;
   enable_interrupts(INT_RTCC);
   enable_interrupts(GLOBAL);
   
   while(TRUE) {
      // ....
      // Your can do anything here while
      // your Leds are blinking in background
      // ....
   }
}


f=fosc*(1/4)*(1/(2^16))*(1/2)*(1/Green_Led_1_blink)=9.53 HZ

fosc = 20MHZ
1 instruction cycle per oscilator cycle = 1/4
time0 increments (2^16) times per interupt
Output is both on and off =2
The Puma



Joined: 23 Apr 2004
Posts: 227
Location: The Netherlands

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PostPosted: Tue Oct 02, 2007 11:36 am     Reply with quote
@Neutone,

Ok, but how can i calculate if i want a 5 hz freq
Which value must Green_Led_1_blink have?
The Puma



Joined: 23 Apr 2004
Posts: 227
Location: The Netherlands

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PostPosted: Tue Oct 02, 2007 3:48 pm     Reply with quote
Strange result for this example
This give a freq of 19.5Khz (scope)
but this should be 39Khz

Do i something wrong???

Code:
#include <18F4620.h>
#use delay(clock=20000000)
#fuses HS,NOWDT,NOBROWNOUT,NOPUT,NOLVP,DEBUG,NOSTVREN,NOPROTECT

//   The cycle time will be (1/clock)*4*t2div*(period+1)
//   In this program clock=20000000 and period=127
//   (1/20000000)*4*1*128=25.6us or 39.0khz

#int_TIMER2
void TIMER2_isr() {
   output_toggle(PIN_C1);
}

void main() {
   setup_timer_2(T2_DIV_BY_1,127,1);
   enable_interrupts(INT_TIMER2);
   enable_interrupts(GLOBAL);
   
   while(TRUE) {
      // ....
      // Your can do anything here while
      // your Led are blinking in background
      // ....
   }
}
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