Reading Input using PDIR(Port Data Input Register)

[rohananand]

Hi,

I have a FRDM-KL46Z Board.I am using Keil uvision.I am trying to read from a switch and turn on a led.When the switch is pressed,the LED should turn on.The code is as follows:

#include "MKL46Z4.h"                    // Device header

void InitLED(void)

{

  SIM->SCGC5=SIM_SCGC5_PORTD_MASK;//Clock to PortD

  PORTD->PCR[5]=256;//PIN 5 of portd as GPIO

  PTD->PDDR=(1u<<5);//PIN 5 of portd as OUTPUT

}

void InitSW1(void)

{

  SIM->SCGC5=SIM_SCGC5_PORTC_MASK;//Clock to PortC

  PORTC->PCR[3]=256;//PIN 5 of portd as GPIO

  PTC->PDDR=(0u<<3);//PIN 5 of portd as INPUT

}

int main()

{

  while(1)

  {

  InitLED();

  InitSW1();

  if(PTC->PDIR==(0u<<3))//Read 0 switch pressed

  {

  PTD->PCOR=(1u<<5);//LED turns on

  }

  else if(PTC->PDIR==(1u<<3))//Read 1 switch not pressed

  {

  PTD->PSOR=(1u<<5);//Led turns off

  }

  }

}

when i download the code on the board,the led turns on without even pressing the onboard button and i dont know what is the problem with the code.

[adriancano · Accepted solution]

Hi,

You need to enable the internal Pull-up for the pin since in the Board are not externally pulled-up. To enable the pull-up you need to write 1 to the PS and PE fields in the PCR register.

Hope this information can help you

Best Regards,
Adrian Sanchez Cano
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[rohananand]

Thanks,This worked.

Can I make any pin as a pullup / pulldown?

Can this switch pin PTC3 become pulldown?

[adriancano]

Hi,

You can select a pull-up or pull-down internal resistor for the pins. There are some pins, like the SDA and SCL for I2C functionality, that are configured as true open drain when selected; in this case the pull up or down internal resistor has no effect on them.

You need to consider also that according to the Datasheet the internal pull-up resistor has a value of 20 to 50 kOhms, it will probably will not be enough for some applications but, like in this case, will help you to ensure a constant value in the pin.

You can pull-down the PTC3 by selecting in the PORTx_PCRn register PE= 1 and PS= 0.

Hope this information can help you

Best Regards,
Adrian Sanchez Cano
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[rohananand]

I am trying to make the PTC3(Switch1)pin as pull-down but it is not working.The code is as follows:

#include "MKL46Z4.h"                    // Device header

void InitLED(void)

{

  SIM->SCGC5=SIM_SCGC5_PORTD_MASK;//Clock to PortD

  PORTD->PCR[5]=256;//PIN 5 of portd as GPIO

  PTD->PDDR=(1u<<5);//PIN 5 of portd as OUTPUT

}

void InitSW1(void)

{

  SIM->SCGC5=SIM_SCGC5_PORTC_MASK;//Clock to PortC

  PORTC->PCR[3]=256|2;//PIN 3 of portc as GPIO and pullup/pulldown+pulldown

  PTC->PDDR=(0u<<3);//PIN 5 of portd as INPUT

}

int main()

{

  while(1)

  {

  InitLED();

  InitSW1();

  if(PTC->PDIR==(0u<<3))//Read 0 switch pressed

  {

  PTD->PCOR=(1u<<5);//LED turns on

  }

  else if(PTC->PDIR==(1u<<3))//Read 1 switch not pressed

  {

  PTD->PSOR=(1u<<5);//Led turns off

  }

  }

}

When I download the above code to the board the led switches on but when i press the switch it does not switch off.The schematic says that the switch is of pull-up type ,can i really use it as a pull-down?

[adriancano]

Hi,

According to the schematic the Button is connected to GND, this means that any time you pressed the value it will drive is 0 (zero). The same way with the internal pull-down the value of the pin is 0 and when you press the button the value will not change.

Using the pull-up the value of the pin is 1 and when you press the button the value will be 0 because the button will short to GND. This means you cannot use pull-down for the button.

Hope this information can help you

Best Regards,
Adrian Sanchez Cano
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------