Strange I2C readings

martynwheeler · Post by **martynwheeler** » Tue May 05, 2020 8:48 am

Hello,

I am using a picoscope to understand some i2c signals from a raspberry pi. The readings that I am getting from the scope do not seem to match what the pi is sending out.

I sent out a packet to a device with address 0x20 but the picoscope is reporting it as 0x16. The data is 0x01 but the scope is reporting it as 0x00. It is as if the serial decoder is reading slightly too early and misinterpreting the data. The pi is able to communicate with the device, so I assume the signal is okay it is just the picoscope misreading things. I have it setup as standard mode and using two logic channels to pull in the data.

Any help would be gladly appreciated, thanks
Martyn

bennog · Post by **bennog** » Tue May 05, 2020 1:17 pm

can you post the .psdata file ?

martynwheeler · Post by **martynwheeler** » Tue May 05, 2020 2:52 pm

I think that I have fixed it. I adjusted the digital threshold to about 1V (default was 1.5V) - it was picking up some noise on the data line and converting it into a 0 (look closely at the beginning of the data). I looked at the signal using a probe and you could see a small dip (I assume the lower bandwidth of the digital channels couldn't cope with this). This was shifting the timings for the decoding.

Thanks

Martyn

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Strange I2C readings

Strange I2C readings

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