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MAKInnovation
Joined: 16 Nov 2010
Posts: 61
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| timer 1 interrupt |
 Posted: Sat Jan 18, 2014 3:59 am |
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Dear Friends;
| Code: |
#define USE_WITH_PC 1
#include <18F452.h>
#fuses HS, NOWDT, NOLVP, PROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, errors)
//RTC variables
#define XTAL_FREQUENCY 20000000
#define TIMER1_FREQUENCY (XTAL_FREQUENCY / 4) // 1 clock tick = 1 instr. cycle = crystal frequency / 4
int32 Ticker;
int8 Seconds=0;
////////////////////////////////////////////////////////////////////////////////
// Initialize RTC
////////////////////////////////////////////////////////////////////////////////
void Initialize_RTC(void)
{
Ticker = TIMER1_FREQUENCY; // initialize clock counter to number of clocks per second
setup_timer_1( T1_INTERNAL | T1_DIV_BY_1 ); // initialize 16-bit Timer1 to interrupt
// exactly every 65536 clock cycles
// (about 76 times per second)
enable_interrupts( INT_TIMER1 ); // Start RTC
}
#org DEFAULT
// Timer 1
#org 0x1000, 0x1FFF DEFAULT
#int_TIMER1
void TIMER1_isr()
{
Ticker -= 65536;// Decrement ticker by clocks per interrupt
if ( Ticker < 65536 ) // If second has expired
{ Ticker += TIMER1_FREQUENCY; // Increment ticker by clocks per second
seconds++; // Increment number of seconds
}
//--------- Some code -----
if (Seconds == 30) {Seconds=0;}
}
////////////////////////////////////////////////////////////////////////////////
// MAIN Program
////////////////////////////////////////////////////////////////////////////////
void main()
{
int8 prev_second;
SET_TRIS_C( 0x8F );
Initialize_RTC();
enable_interrupts( GLOBAL );
while(1)
{
if (seconds != prev_second)
{
prev_second = seconds;
// -------- some code ----------
delay_ms(10);
}
}
}
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I am using a very common timer code for my project. this code generates interrupt about 76 times per second.
which is slow for some of my calculation.
I want to generat interrupt about 800 times per second. How can i do this. Kindly resolve my issue.
Regards;
Ashraf |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19359
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| Posted: Sat Jan 18, 2014 4:19 am |
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Use timer2.
Unlike the other timers, this one can be programmed for a specific count, rather than 65536.
setup_timer_2(T2_DIV_BY_4, 155, 10);
Will give an interrupt at 801Hz.
(((20000000/4)/4)/156)/10 = 801.28
However a much nicer number to work with is 1000Hz, since this divides evenly into the master clock/4.
setup_timer_2(T2_DIV_BY_4,249,5);
Remember though that it takes typically 60 instructions to get into and out of the interrupt handler, so the chip will be spending about 1.5% of it's time just handling the interrupt.
Best Wishes |
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