I2C3 not able to establish communications

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Hi there,

I have recently acquired the development quit and I am making the first tries. I’m trying to use the bus I2C3. In order to do so, I have connected the R156 and R157 that are not populated in imx6rex. Now, I have connected an temperature I2C sensor to the J34 connector, using 8,10 pins for SDA and SCL and 1 and 9 to power up the sensor. As I am not accessing the device (I have used ‘ i2cdetect 2′ command to do so) , I have checked the schematic and I have seen this:

I2C

Does really R45 and R44 affect the communication? Or am I forgetting something else?

Thanks in advance!

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Best Answer
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Good news, finally I have managed to use the bus I2C3. Basically I have changed the image I was using, from factory linux OS to this one, and now works :)

To test the bus, I have used a HIH_6138 sensor. I have edited a python script that displays the humidity, and used it first in the BeagleBone to see that it was working fine, and later in the imx6rex, here you have the script. (you need python-smbus package to run it).

To have access to the I2C3, I have used the connector J34, the pins 1 and 9 to supply voltage to the sensor and, 8 – 10 pins for SDA/SCL.

Hope is helpful,

Iñigo

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No I haven’t. I have a look tomorrow and I’ll write again with more info.
Thanks.

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Hi,

I have connected the oscilloscope to the I2C3 SDA and SCL. I’m seeing something “strange” (to me) in the SCL bus. Bassically it doesn’t reach to 0V when draws the down edge. The voltage range in which switches is ~2.2 and 3.3v. I guess that this may be a reason to not to see the sensor I’m connecting to the bus, is not able to syncronize to clk because is not properly generated.
Am I right, or you see something else that is strange?

Here you have some pictures of SCL signal:
(including links ’cause I think they are not properly displayed)

SCL zoom out

link: http://pbrd.co/1upYuYf

SCL zoom in

link: http://pbrd.co/1upYFTg

SDA images:

SDA zoom in

link: http://pbrd.co/1upYNSK

SDA zoom out

link: http://pbrd.co/1upYTKe

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Hmm, works oki on our board.

enter image description here

Measured on:

J34 – pin 8 – I2C3_SDA

J34 – pin10 – I2C3_SCL

Command line:

i2cdump -r 0-0xf 2 0×51 b

Did you disconnect your sensor from the connector during measuring?

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Yes of course. BTW which OS are you using? I have started working with the one that cames in the SD card, Ubuntu 13.04

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It should work with the Kernel you have. We are doing some test with touchscreen, so we use this: http://www.imx6rex.com/download/design-files/imx6_rex__development_baseboard/v1i1/firmware/binaries/imx6rex-uImage-lvds-clock-TSC2007-support-31-JUL-2014

Our files system is: http://www.imx6rex.com/rex-uploads/imx6rex-xubuntu-13-04-production-04-AUG-2014.tar

There are only pull up resistors connected to the I2C3 bus, so if you measure between GND and SDA or SCL, there really should be 3V3. Have you disconnected R156 and R157? If they are connected, they could influence the signal.

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is it working now oki?

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R156 and R157 are not popullated any more, and still not working. I’m switching to I2C2 bus, using J4 or J3 port. This cable ( PCI-E 1X) should allow me to connect to them, I guess.

PCI cable

But definitively would like to fix I2C3, any suggestion??

Thanks again,

Iñigo

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Please Inigo, what uboot and kernel do you use? Is it ours? Please could you send me the booting logs? (uboot + kernel). Thank you.

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Hi Inigo, please do not fit the R156 and R157. I2C3 should work without it. That should help. Robert

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I have tried before without them, but nothing.

Iñigo

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I am very happy it’s working oki :) Thank you very much Inigo for sharing your script.

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I will have a look by scope (I will try tomorrow, but can not promise). Maybe you can try to probe it too – just place oscilloscope on the connector and have a look if you can see the waveforms (do not connect your sensor, just run the I2C detect command – you should be able to see clock and I believe also some data, possibly try different I2C commands). I am not sure what Linux do you use, but because there is no device connected, it is possible that the I2C may need to be initialized in software first. Did you try scope?

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