TWI with TCA6424A

[Michal]

Hi. I got TCA6424A IC which communicates through i2c. I tried to use that with nordic but it doesnt respond. I used simple twi scanner application which should print address of my device but it didnt work. For now I pull up sda and scl with 10k resistor. I tried pulling to 2V, 3.3V and 5V and no pull but none of this worked. I configure twi speed to 100kbps.

Is it possible that somehow i2c from IC is not compatibile with nordic twi protocol ? Or should search for problem in hardware? Other person from project tested this IC with arduino on similar setup and it was responding.

[Sylvain]

Hi Michal,

if you have an oscilloscope try to check your SCK and SDA lines to be sure that you have the right signal.

Can you post your main code ?

Sylvain.

[Michal]

Thanks. As I mentioned I am using twi_scanner sample application from nordic SDK. I will have logic analyzer soon but for now I dont have any sophisticated tools. Although as I tak unmodified example from SDK 14.2 I expect that signals are correct. I also tried other sdk - 11, 12, 12.3 but there were no difference.

[Sylvain]

Sorry, I badly read your first post. In fact, if you just want to know the adress of your devices the I2C scanner is appropriate.

The external pull-up aren't obligatory since the nRF implement internal pull up.

So, the best way to fix your problem is to found an oscilloscope and check your hardware configuration.

[Jakub Rzeszutko]

Hi,

TWI scanner is the best what you can use to check I2C communication. If it does not work I am affraid you need a logic analyzer or oscyloscope.

[Michal]

Hi Kuba,

Can you confirm that is not possible that twi is incompatible with IC that communicates over i2c? Thanks

[Jakub Rzeszutko]

Hi,

I do not see any obvious inconsistency, our chip and TCA6424A are supporting 7 bit addressing.

Did you connect TCA6424A  to our DK? Which PINs did you use?

[Michal]

I was using default gpios as in example. I think it was 27 for SCL and 26 for SDA. I will try modifying hardware setup and post here any results later. Thanks for help.