I2C clock frequency problem

[Manjunath K S]

Hi,

I am using NRF52832 development board , to which i have interfaced LIS3DSH accelerometer sensor(3.3V i2c)

when i  configure it for 1600 sampling rate and all the axis enabled , i am not able to get any data .

could anyone help with this problem.

also the I2c clock frequency, as shown in below image, while i am capturing data when i observe in oscilloscope or logic analyzer , clock frequency is showing 200 all the setting is for 400KHz.

what could be the problem for this or is there any other way i need to follow to set the clock to 400KHz.

help me ASAP...

Thank you

[haakonsh]

"also the I2c clock frequency, as shown in below image, while i am capturing data when i observe in oscilloscope or logic analyzer , clock frequency is showing 200 all the setting is for 400KHz."
That's unlikely, I think you're measuring the clock frequency incorrectly.


Why have you enabled pulldowns on your IO pins?

[Manjunath K S]

actually that's not the part of code , sorry excluding that is the actual code

[awneil]

It is a standard feature of the I2C bus that it operates at the speed of the slowest attached peripheral

[Manjunath K S]

tqs  awneil but peripheral supports 400K clock

[awneil]

But your test demonstrates that the issue is not to do with your software configuration, or an SDK bug, in the nRF chip?

Does your peripheral default to 200kHz, and need to be configured to change to 400 ... ?

[Manjunath K S]

By default lis3dsh peripheral will support 400K fast mode, it was working in other development kit(also clock in other dk was also reflected) like renesas and stm eval board.

that's  y i didn't get to know the actual problem and asking for your help.

[haakonsh]

The GPIO expander is connected to P0.13 - P0.20: I/O expander for buttons and LEDs. And I believe they should work at 400kHzthrough the IO expander.

awneil said:

Does your peripheral default to 200kHz, and need to be configured to change to 400 ... ?

I've not found anything in the LIS3DSH's specs that hints to a configurable I2C clock.

Paraphrased from its spec, "The LIS3DSH supports fast I2C mode with clock speeds up to 400kHz", but, it does not say anywhere in its specification that its I2C slave runs at 400kHz, rather it supports 'fast mode I2C'.

What you're seeing on SCL is the I2C slave clock stretching down to 200kHz.

This is most likely the expected behavior of this device. 

[Manjunath K S]

Thanks haakonsh , but same slave i am using withother development kit /microcontroller eg: Renesas S5D9 and stm32eval board , also raspberry pi , while it is working in all those environment for same code and configuration giving expected clock frequency in the logic analyzer , that's the reason i came to you people.

[awneil]

The LIS3DSH is an ST Product - so you probably need to go back to ST to ask them what might cause their product to behave like this.

[Manjunath K S]

if it is working in other 3 boards and not in Nordic , they will surely ask me to check with you people , to ask whether there is any problem with code or not.

[awneil]

Indeed - and you can refer them to this thread.

[awneil]

So far, I think you've only shown logic analyser (ie, digital) traces ?

Have you looked at the clock with an oscilloscope - to see if there are any weird analogue effects going on?

eg, if you have extremely long rise times ... ?