I2C Reliability -

[RichardP]

Hi all,

Using a ESP32 connected to two devices on I2C I get very erratic behaviour. I have a PCF IO expander and a SI570 Controllable oscillator.

I have the I2C lines on IO 22+23 and a 330ohm pullup resistors. On first power-up, it seems to work, but then things go bad.

I2Ctext_nack.png (55.63 KiB) Viewed 5284 times

Attached is from a Logic analyser.


The transaction to the IO expander works 99% of the time, but that is simple.

I2Ctext_good_expander.png (6.09 KiB) Viewed 5284 times

First power-up on the SI570 Oscillator, although I do have to re-try transactions once. (there is one NACK instead of ALL nack)


In the bad cases, I get NACK and then I try 10 times to write to the address. The Bus recovers after a while and I have no idea why.

I2Ctext_bad_si570.png (5.67 KiB) Viewed 5301 times

[ESP_Sprite]

Not sure if your pictures work... but 330 ohm seems awfully low for pullup resistors. Maybe try making these a bit higher to, say, 2K2 or 1K or so?

[RichardP]

Hmm.. pictures went funny... The pullup is a 3k3 (it was a typo) - but its not the ESP32. I have got down to the Si570 not working properly if the CLK+ line is not terminated. (I left it floating, I added a load to the CLK+ line and it seems to be better)

Regards,
Richard

[ESP_Sprite]

Check, glad to hear you solved it!

[RichardP]

Unfortunately not... I thought it was working... It ran for hours until I powered off for the night. The next day the problems were back.

I put the I2C bus on a scope and I can see glitches on the bus.. they are always there, just some slave devices are more sensitive than others. I have cloned the latest ESP-IDF code but yet to try (I am away and will only be back at the weekend)

In the meantime I have added a bitbanged software I2C driver to my project to see if things change.

Best Regards,
Richard