PIC:how can we get 1 ms interrupt using 16bit timer

frequencymicrocontrollerpictimer

I am using PIC24FJ256GB106 controller.I am setting configuration bit for internal frequency to FNOSC_FRCPLL.

I have confusion to this configuration bits that Am i getting 8MHZ or 16MHZ or 32MHZ ?

if I want timer(16bit) interrupt at every 1 ms then which frequency i have to use ? FOSC or FCY?

When i am setting FNOSC_FRCPLL configuration bit then what is FOSC and FCY?

Best Answer

FNOSC_FRPLL means your ultimate clock will be the output of the PLL module.

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Summarizing from the PIC24F family reference manual:

6.8.3 FRC Oscillator with PLL Mode (FRCPLL)

The output of the FRC postscaler block may also be combined with the 4x PLL to produce a nominal system clock of either 16 MHz or 32 MHz. Although somewhat less precise in frequency than using the Primary Oscillator with a crystal or resonator, it still allows high-speed operation of the device without the use of external oscillator components.

The FRCPLL mode is selected whenever the COSC bits are ‘001’. In addition, this mode only functions when the direct or divide-by-2 FRC postscaler options are selected (RCDIV2:RCDIV0 = 000 or 001).

Related Solutions

Electronic – C18 Timer0 timing calculation using MCC18

The answer is simple. When the overflow bit occurs and the interrupt is raised, we need to first write the counter to TMR0 and reset the TMR0IF flag.

This solution works:

#pragma code 
#pragma interrupt high_priority_interrupt 
void high_priority_interrupt()
{
    if (INTCONbits.TMR0IF)              //TIMER0 overflowed
    {
        //Stuff
        second += 1;
        if (second == 60)
        {
            minute += 1;
            second = 0;
        }

        if (minute == 60)
        {
            measure_and_switch();
            minute = 0;
        }

        WriteTimer0(CLOCK_TICK);        //Write the count to TMR0.
        INTCONbits.TMR0IF = 0;          //Clear TIMER0 overflow bit.
    }
}

I hope this helps anyone. :-)

Electronic – Clarification on what the max freq of PIC24FJ64 is

The datasheet is correct, as they usually are. The PIC 24F family can run at a maximum instruction cycle rate of 16 MHz, which can be expressed as 16 MIPS (Million Instructions per Second). This processor requires 2x clock over the instruction rate, so the maximum clock is 32 MHz. You can achieve 32 MHz clock with a 8 MHz crystal and the 4x PLL. That will result in 16 MHz instruction clock.

Best Answer

Related Solutions

Electronic – C18 Timer0 timing calculation using MCC18

Electronic – Clarification on what the max freq of PIC24FJ64 is

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