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FRDM-K22F PIT GPIO Toggle Frequency Problem

Question asked by Jack Xu on Jul 28, 2016
Latest reply on Aug 1, 2016 by Jorge Antonio Alcala Vazquez

Hi there,

 

Recently i'm trying to write some routine with PIT control GPIOs, but it runs in disorder. Part of PIT0_IRQHandler routine as follow:

 

/****************************PIT0_IRQHandler***********************************************/

cnt1 = (cnt1 + 1) & 0xff;

const1 = 500;

/**********************************************************************************************/

if (const1 >500)

{

     if(cnt1 < 64)

     {

          GPIO_ClearPinsOutput(BOARD_PIN1_GPIO, 1U << BOARD_PIN1_GPIO_PIN);

     }

     else if (cnt1 < 128)

     {

          GPIO_SetPinsOutput(BOARD_PIN1_GPIO, 1U << BOARD_PIN1_GPIO_PIN);

     }

     else

     {

          GPIO_ClearPinsOutput(BOARD_PIN1_GPIO, 1U << BOARD_PIN1_GPIO_PIN);

     }

}

else

     GPIO_ClearPinsOutput(BOARD_PIN1_GPIO, 1U << BOARD_PIN1_GPIO_PIN);

/***************************************************************************************************/

if (cnt1 < 128)

{

     GPIO_ClearPinsOutput(BOARD_PIN2_GPIO, 1U << BOARD_PIN2_GPIO_PIN);

}

else if(cnt1 < 192)

{

     GPIO_SetPinsOutput(BOARD_PIN2_GPIO, 1U << BOARD_PIN2_GPIO_PIN);

}

else

{

     GPIO_ClearPinsOutput(BOARD_PIN2_GPIO, 1U << BOARD_PIN2_GPIO_PIN);

}

/*****************************************************************************************************/

if(cnt1 > 256)

{

     cnt1 = 0;

}

/*****************************************************************************************************/

 

 

/********************************Main****************************************************************/

    PIT_SetTimerPeriod(PIT, kPIT_Chnl_0, 2000);

 

and set my bus clock @ 50MHz, then the PIN1's frequency should @50MHz/2000/256=97.66Hz

But read from my scope is @48.83Hz

also the PIN2's frequency is the same as the PIN1

@. (the first 10.24ms is ok, but there is another 10.24ms, do not know why there is another 10.24ms)

 

Thanks in advance!

-Jack

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