Pull down SDA pin i2c

[Hkhan7861]

Good day

I am developing on the nrf9160dk with a tag reader using i2c and am wanting to know if there is a function to pull down the SDA or SCL pins during operation in order to wake up the slave device.

Thank you in advance.

Kind regards,

Hassan

[Hkhan7861]

Hi, thank you for the reply. This is the extent of what the documentation states.  Thank you !

6.1.1 Start condition Start is identified by a falling edge of serial data (SDA) while the serial clock (SCL) is stable in the high state. A Start condition must precede any data transfer command. The device continuously monitors (except during a write cycle) the SDA and the SCL for a Start condition, and does not respond unless one is given.

www.st.com/.../st25dv04k.pdf

[Hkhan7861]

HI, do you mind sending the name or a link to that function so I may see how it works.  I can't seem to find it

Yes, I have used instruments to test and have found that by using an internal pull-up resister, the pin signal level doesnt drop enough.

[Vidar Berg]

Hkhan7861 said:

I am still not able to find this function.  I am not sure you understand my question.  Please refer me to where the start condition is handled.

There is no function for this because it is handled in HW.

[Hkhan7861]

Oh I see okay thank you ! so would I just need to use 

nrf_twim_task_trigger(p_twim, NRF_TWIM_TASK_STARTTX) and the startup condition will be handled?  

Thank you .

 

[Vidar Berg]

The TWIM peripheral must be configured to transmit data before you can trigger the start task. It is easier to just use the driver APIs to start a transaction as it will take care of the configurations for you.

[Hkhan7861]

Good afternoon

By driver API's, do you mean this function.

     struct i2c_msg *DevFnc ;

     DevFnc->buf = &devSelCode;

     DevFnc->len = 8;

     DevFnc->flags = 1;

     i2c_nrfx_twim_transfer(i2c_dev,DevFnc,1, 0x53 );

If so, are there any samples where I can see the use of this.

Kind regards,

Hassan

[Vidar Berg]

Yes, this is our function to start a TWI transfer. However, in general, we recommend to use the Zephyr's driver APIs when possible (https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/hardware/peripherals/i2c.html). You can have a look at the i2c_fujitsu_fram driver sample in the Zephyr tree for an example of how this API can be used.

Kind regards,

Vidar

[Hkhan7861]

Good day,

I've attempted using these functions and APIs and when I test the board with the multimeter, pin 30 and 31 (my i2c2 pins) get zero voltage output.  Do the pins start the output in the prj file or when a write/read sequence is initiated?

Kind regards,

Hassan

[Hkhan7861]

My code is as follows:

main.c

#include 	<zephyr/zephyr.h>
#include 	<drivers/i2c.h>
#include	<stdio.h>
#include 	<nrfx_twim.h>
#include 	<C:\nordicsemi\v2.1.1\modules\hal\nordic\nrfx\hal\nrf_gpio.h>
#include 	<hal/nrf_twim.h>





/** I2C address to be used for ST25DV Data accesses. */
#define ST25DV_ADDR_DATA_I2C                 0x53
/** I2C address to be used for ST25DV System accesses. */
#define ST25DV_ADDR_SYST_I2C                 0x57


void Delay(int n)
{
   int c, d;
   
   for (c = 1; c <= n; c++)
       for (d = 1; d <= n; d++)
       {}
       
   return 0;
}



void main(void)
{   
	// *************START************* //  
	

  const struct device * i2c_dev;
   i2c_dev = DEVICE_DT_GET(DT_NODELABEL(i2c2));
  if (i2c_dev == NULL) {
		printk("Unable to bind !\n");
		return;
	 }

	 //************** DEVICE SELECT CODE**************//

	const uint8_t devSelCode[8] = {1, 0, 1, 0, 0, 1, 1, 0};
	 
	int err1 = i2c_write(i2c_dev,devSelCode,8,ST25DV_ADDR_DATA_I2C);
	printk("Device select msg: %d", err1);

     
	 
	
}



prj


CONFIG_STDOUT_CONSOLE=y
CONFIG_PRINTK=y

CONFIG_I2C=y

# CONFIG_LOG=y

Is there possibly something wrong in my configuration that I am not seeing an output in my specified i2c2 pins?  Thank you for your help!

[Vidar Berg]

It seems like you don't have external pull-ups on the SDA and SCL lines as you measure 0 V on both . In that case, you will need to enable the internal pull-up resistors by adding the bias-pull-up property to your pin assignment in the device tree.

 &pinctrl {
	i2c2_default: i2c2_default {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 0, 30)>,
				<NRF_PSEL(TWIM_SCL, 0, 31)>;
				bias-pull-up;
		};
	};

	i2c2_sleep: i2c2_sleep {
		group1 {
			psels = <NRF_PSEL(TWIM_SDA, 0, 30)>,
				<NRF_PSEL(TWIM_SCL, 0, 31)>;
			low-power-enable;
		};
	};

};

[Hkhan7861]

HI

This has helped!  Am now seeing an output when the program starts as well as the drop of output on the SDA line when writing to the i2c2 .  However, the write function still returning an error value.  Other than the slave address or device function code being incorrect, are there any other reasons for the function to fail?

[Vidar Berg]

Hi,

Can you turn on logging to see what the error is?