BQ24261M: I2C Problem, stop condition missing

Hey Gerhard,

I am looking into this question, but in the mean time, have you tried operating at the Standard Mode clocking rate of 100kHz? 

I am just curious if this is clocking spec issue.

Regards,

Joel H

Hi Joel,

Indeed the error rate drops after I reduced the bus speed to 300kHz, and you are right, with 120kHz it looks very fine, but I need some time to get good results.

I thought that the signals looking quite good.

With best regards

Gerhard

Hey Gerhard,

Yes that sounds right. You may want to reduce it to the point where the issue is not longer present. 

You must also consider your bus capacitance and pull-up strength as you reduce the clocking frequency just to make sure you continue to stay in time. 

Here is an app note showing calculation for pull-up resistance strength for I2C. Click here

The last thing is to make sure your master/host can support clock stretching. 

Hi Joel,

I know, so I don't use a simple pullup. I use current mirrors instead. This gives nice edges as you can see on my Pictures.

I also think, that I fullfill all specs of the data sheet. I have some other Chips on the bus, no Problems at all.

Slowing down the bus for tests is ok, but I hope to run it at 400kHz as all Chips on the bus are ready for that Speed (according to the data Sheets).

With best regards

Gerhard

Hey Gerard,

I would also check to make sure your host can support clock stretching.

Regards,

Joel H

Sorry for the delay.

Here the capabilities of my TWI Interface according to the data sheet of the processor = master:

So I think, this is ok.

New observations:

The System sits in a closed room, nobody was there, sometimes it works for days, but today it Fails 3 times So the period between failure gets shorter or something happens in our universe .. strange behaviour.

With bet regards

Gerhard