PIT as timer interrupt for DAC- KL25Z

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PIT as timer interrupt for DAC- KL25Z

440 Views
ofiryaish
Contributor II

HI,

 I tried to send signal with DAC in fixed times using PIT timer interrupt (the value of the signal is changing as the PIT interrupt occur). I configured the PIT timer to interrupt in each 1ms and what I get in oscilloscope which test the signal  is 

that the signal is changed in any 5ms and not 1ms as i thought.

here is the setting of the the clocks, DAC and the PIT Interrupt.

please tell me if  something with my setting is wrong  

 

void InitPIT(){

SIM_SCGC6 |= SIM_SCGC6_PIT_MASK; //Enable the Clock to the PIT Modules

// Timer 0

PIT_LDVAL0 = 0x0000BB80; // setup timer 0 for 1msec counting period

PIT_TCTRL0 = PIT_TCTRL_TEN_MASK | PIT_TCTRL_TIE_MASK; //enable PIT0 and its interrupt

PIT_MCR |= PIT_MCR_FRZ_MASK; // stop the pit when in debug mode

enable_irq(INT_PIT-16); // //Enable PIT IRQ on the NVIC

set_irq_priority(INT_PIT-16,0); // Interrupt priority = 0 = max

}

void InitDAC(){

//When the DAC is enabled and the buffer is not enabled, 

//the DAC module always converts the data in DAT0 to analog output voltage.

// pin PTE30 is by default (ALT0) configured as DAC0_OUT

//VDDA reference voltage (Use this option for the best ADC operation).

SIM_SCGC6 |= SIM_SCGC6_DAC0_MASK; //DAC0 Clock Gate Control

DAC0_C0 |= DAC_C0_DACEN_MASK + DAC_C0_DACRFS_MASK + DAC_C0_DACTRGSEL_MASK + DAC_C0_LPEN_MASK; 

}

void PIT_IRQHandler(){
if (state==2){ //if state=2 deliver signal out will enter each 1ms (I don't know why the scope show 5ms)
sampleNumOut=sampleNumOut%41;
DAC0_DAT0H = ((int)samplesArray[sampleNumOut] & 0xF00)>> 8; //deliver the signal of the DAC out (DAT0H=DAC                                                                                                                                                                DATA High Register)
DAC0_DAT0L = (int)samplesArray[sampleNumOut] & 0x0FF; //deliver the signal of the DAC out (DAT0L=DAC DATA                                                                                                                                                                      LOW Register)
sampleNumOut++;
}
// When software trigger is selected, a conversion is initiated following a write to SC1A
ADC0_SC1A = POT_ADC_CHANNEL | ADC_SC1_AIEN_MASK; //here for other purpose.
PIT_TFLG0 = PIT_TFLG_TIF_MASK; //clear the Pit 0 Irq flag
}

thank you

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101 Views
jorge_a_vazquez
NXP Employee
NXP Employee

Hi Ofir

PIT module take bus speed as the reference clock, How do you have setup the bus speed? depending on this speed, you will have to load a value to PIT_LDVAL0. Also, I didn't see where you are clearing the MDIS bit of the PIT_MCR register, this field must be enabled before any other setup is done.

Best regards

Jorge Alcala

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