Whether I should add external pull-up resistor or not for I2C pin? (IDFGH-8310)

[BrandonStudio]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

General issue report

You have contradictory versions about this:

On https://github.com/espressif/esp-idf/blob/36f49f361c001b49c538364056bc5d2d04c6f321/tools/test_apps/peripherals/i2c_wifi/README.md, you say:

Note: It is recommended to add external pull-up resistors for SDA/SCL pins to make the communication more stable, though the driver will enable internal pull-up resistors.

whereas on https://github.com/espressif/esp-idf/blob/36f49f361c001b49c538364056bc5d2d04c6f321/examples/peripherals/i2c/i2c_tools/README.md, you say:

**Note: ** There’s no need to add an external pull-up resistors for SDA/SCL pin, because the driver will enable the internal pull-up resistors itself.

Which one should I believe?

[mythbuster5]

@BrandonStudio You can see the update date is different.

Well, let me make a conclusion, the docs say no need to pull-up external on theory is correct, because we do have internal pull-up to support this. The reason why new docs say user should pull up is because we found the I2C slave users used are very very different. Sometimes the capacity will influence the frequency that user should adjust resistor. Sometimes users feel internal pull-ups are not strong enough.

So, new docs and technical reference manual both say user should choose proper external pull-up resistors. Of course, the old one is out of date and need to be updated, thanks so much.

[BrandonStudio]

OK, I hope you can update all related docs to make it consistent and unconfusing.

[BrandonStudio]

@mythbuster5 well, actually, I see they were modified by the same commit c056861 on July 14

Anyway, you may update it.