Hi,

I'm making some progress with a simple clock application, but cannot get
TIMER1, with a 32.768Khz watch crystal on the T1OSO/T1OSI pins to work
at all. The code below works if I un-comment the TIMER0 parts marked
"A", but when I use my TIMER1 code (marked "B"), the timer overflow
interrupt never gets called. My oscilloscope shows the 32.768khz xtal is
oscillating nicely.

I'm going back to study the reference manuals now, but if anyone can
spot the goof-up, I'd be really grateful.

Peter Moreton



/*
 * The following code will flash LEDs connected to PORTC of a  PIC18F452
microcontroller, using timer1
 */

#include <p18f452.h>
#include <timers.h>

#define NUMBER_OF_LEDS 8

void timer_isr (void);

static unsigned char s_count = 0;

/*
 * For PIC18xxxx devices, the low interrupt vector is found at
000000018h.
 * Change the default code section to the absolute code section named
 * low_vector located at address 0x18.
 */

#pragma code low_vector=0x18
void low_interrupt (void)
{
  // Inline assembly that will jump to the ISR.
  _asm GOTO timer_isr _endasm
}

// Returns the compiler to the default code section.
#pragma code

/*
 * Specifies the function timer_isr as a low-priority interrupt service
 * routine. This is required in order for the compiler to generate a
 * RETFIE instruction instead of a RETURN instruction for the timer_isr
 * function. In addition, it ensures that PROD special function register
 * will be saved.
 */

#pragma interruptlow timer_isr save=PROD

void timer_isr (void)
{
  static unsigned char led_display = 0;

        // Clear the TMR1 interrupt flag to avoid processing the same
interrupt multiple times

        //INTCONbits.TMR0IF = 0;        // A: Original TIMER0 reset
Interrupt flag code

        PIR1bits.TMR1IF=0;              // B: Couldn't find
"INTCONbits.TMR1IF", maybe this is right?

  s_count = s_count % (NUMBER_OF_LEDS + 1);
  led_display = (1 << s_count++) - 1;
  PORTC = led_display;
}

void main (void)
{
  int count;

  TRISC = 0;
  PORTC = 255;

  // Enable the TMR1 interrupt, setting up the timer as an external
32.768 khz, 16-bit clock

  //  OpenTimer0 (TIMER_INT_ON & T0_SOURCE_INT & T0_16BIT);
// A: Original Timer0 code that works OK

  OpenTimer1 (TIMER_INT_ON & T1_OSC1EN_ON & T1_PS_1_1 & T1_SYNC_EXT_OFF
& T1_16BIT_RW); // B:

  INTCONbits.GIE = 1;           // Enable global interrupts

  while (1)
  {
                ;
  }

}

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