As you can see, my i2c clock has some pulses at 3.3v and then many pulses at like 3v or maybe even less. The data is doing something funny too.

devices on the bus aren’t responding.

thanks!

 

Something is disturbing your power supply. You can see that because the Data high voltage is only determined by a pullup resistor to the power supply.
Are the grounds properly connected between the two devices?
What does the 3.3V supply look like on the scope?
Are you sure that the SDA and SCL outputs are both set to open-drain?

 

Can you post the schematic? Maybe you wired some connections incorrectly?

 

Can you post the schematic? Maybe you wired some connections incorrectly?

Seems poor Ground / Supply or something connecting SDA with SCL.
Scope shows one signal is coupled with the other.

 

I can post the schematic tomorrow probably. I checked and there is about 9.9k between sda and scl (about double their individual pull ups).

Are you saying the power could be browning out? I’ll put the 3.3v on the scope tomorrow morning.

This is all on a pcb with a strong solid ground plane.

Same firmware is uploaded to a different board design with same processor and similar i2c devices with no trouble. So I don’t think it’s the settings of the pins but I’ll ask the firmware engineer to double check.

thanks everyone.

 

Scope shows one signal is coupled with the other.

Now I see it, they are connected in some way

 

I checked the 3.3v, it’s solid.

I removed the pull up resistors and it works now.

using a BMD-341 from ublox. Maybe that module has internal pull-ups. I’ll have to look into that.

thanks everyone for looking providing suggestions!

 

I checked the 3.3v, it’s solid.

I removed the pull up resistors and it works now.

using a BMD-341 from ublox. Maybe that module has internal pull-ups. I’ll have to look into that.

thanks everyone for looking providing suggestions!

If it works without the pullup resistors, then there is definitely a fault.
I2C does not work without the pullup resistors.

 

That’s why I think the bmd-341 is pulling them high.