problem using timers with PIC18F4550, help needed?

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elrayes

Joined: 03 Jun 2008
Posts: 164
Helped: 8
Location: Egypt

09 Jun 2009 14:39 c18 timer 0

Hi all

I just want to use timer0 in PIC18F4550 and really i'm tired of reading and trying, beside i'm a very bad programmer, so try to help me in this code, I'm using MPLAB C18 compiler, this code is used to light some LED's on PORT D when the timer expires, i used ISR to implement all this, the code building is fine and downloaded on the target but the MCU isn't working:

#include<p18f4550.h>
#include<stdlib.h>
#include<timers.h>

#pragma interrupt high_isr
#pragma interruptlow low_isr

void init_int(void)
{
//configuring interrupts
INTCON = 0xA0;
INTCON2 = 0x04;
}

#pragma code high_vector=0x08
void interrupt_at_high_vector(void)
{
_asm goto high_isr _endasm
}
#pragma code

#pragma code low_vector=0x18
void interrupt_at_low_vector(void)
{
_asm goto low_isr _endasm
}
#pragma code

#pragma interrupt high_isr

void high_isr(void)
{
if(INTCONbits.TMR0IF == 1)
{
INTCONbits.TMR0IF = 0;
PORTD = 0x0f;
}
}

#pragma interruptlow low_isr
void low_isr(void)
{
}

#pragma code

int x = 0x0000;
void main(void)
{
TRISD = 0x00;
LATD = 0x00;

OpenTimer0( TIMER_INT_ON & T0_16BIT & T0_SOURCE_INT & T0_PS_1_8);
WriteTimer0(0x0000);

while(1)
{
high_isr();
}
}

hope someone could solve this.
thanks

L Varalakshmi

Joined: 28 May 2009
Posts: 15
Helped: 2

10 Jun 2009 9:51 pic18f4550 timer

Just an advice....

You want the LEDs to glow based on the Interrupt concept and not the Polling concept. But here you are calling the function "high_isr" in the while loop, which is an ISR. Once the timer expires it will automatically calls the ISR.

Once check with the interrupt and polling concepts to make your program work.

ravimarcus

Joined: 09 May 2005
Posts: 204
Helped: 19
Location: Bangalore, INDIA

14 Jun 2009 11:27 pic18f prescaler timer 2 not working

Have you assigned high priority to the timer0 interrupt?

Cheers

Ravi

elrayes

Joined: 03 Jun 2008
Posts: 164
Helped: 8
Location: Egypt

14 Jun 2009 12:05 latbbits.latb0

actually i changed the above code to another one i found in C18 examples by microchip and still not working and really i'm in a mess, this is the new code:

#include <p18f4550.h>
#include<timers.h>

//----------------------------------------------------------------------------

void main (void);
void InterruptHandlerHigh (void);

union
{
struct
{
unsigned Timeout:1; //flag to indicate a TMR0 timeout
unsigned None:7;
} Bit;
unsigned char Byte;
} Flags;

//----------------------------------------------------------------------------
// Main routine

void
main ()
{
Flags.Byte = 0;
INTCON = 0x20; //disable global and enable TMR0 interrupt
INTCON2 = 0x84; //TMR0 high priority
RCONbits.IPEN = 1; //enable priority levels
TMR0H = 0; //clear timer
TMR0L = 0; //clear timer
T0CON = 0x87; //set up timer0 - prescaler 1:8//0x82
//T0CON = 0xB8; //no pre-scaler assigned
//T0CON = 0b10011000; //no pre-scaler assigned
INTCONbits.GIEH = 1; //enable interrupts
TRISB = 0;
TRISA = 0;
//LATA = 0x00;

while (1)
{
PORTA = 0x01;
if (Flags.Bit.Timeout == 1)
{ //timeout?
Flags.Bit.Timeout = 0; //clear timeout indicor
LATBbits.LATB7 = LATBbits.LATB0; //copy LED state from RB0 to RB7
}
}
}

//----------------------------------------------------------------------------
// High priority interrupt vector

#pragma code InterruptVectorHigh = 0x08
void
InterruptVectorHigh (void)
{
_asm
goto InterruptHandlerHigh //jump to interrupt routine
_endasm
}

//----------------------------------------------------------------------------
// High priority interrupt routine

#pragma code
#pragma interrupt InterruptHandlerHigh

void
InterruptHandlerHigh ()
{
if (INTCONbits.TMR0IF)
{ //check for TMR0 overflow
INTCONbits.TMR0IF = 0; //clear interrupt flag
Flags.Bit.Timeout = 1; //indicate timeout
LATBbits.LATB0 = !LATBbits.LATB0; //toggle LED on RB0
}
}

high priority interrupts enabled
anyone can help??

thanks in advance

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14 Jun 2009 12:05 Ads

ravimarcus

Joined: 09 May 2005
Posts: 204
Helped: 19
Location: Bangalore, INDIA

14 Jun 2009 12:12 c18 timer interupt

1. I am not that good in C. Have you assigned timer0 interrupt to high priority?
2. Have you simulated in MPLAB SIM? You will get to know the problem.

Cheers

Ravi

L Varalakshmi

Joined: 28 May 2009
Posts: 15
Helped: 2

15 Jun 2009 9:58 pic18f4620 prescaler timer0

Check with the configuration settings, your board should support the oscillator settings you provide in that.
Ex: incase you gave 4*HSPLL and crystal oscillator is at around 25MHz, it gives around 4*25MHz = 100MHz. But if the controller you are using supports less than this (<100MHz) your code doesn't work with that.

Also, you didn't load values to timer registers(TMR0L)
Initialise every time the registers in the ISR.