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Should I connect the CS pin on an ILPS22QS sensor to enable I2C?

In order to enable the I2C interface, on page 25 of the datasheet it says that the CS pin of SPI must be tied high by connecting it to VDD_IO.

Moreover, on page 35 a control register (IF_CTRL) is mentioned that allows connecting/disconnecting a pull-up resistor for the CS pin. By default (bit 0) the pull-up resistor is enabled.

So, by default I2C is already enabled. Do I have to do nothing with CS? Should I connect the CS pin to VDD_IO or leaving it floating?

Page 25: enter image description here

Page 35: enter image description here

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No, you do not have to tie the pin to Vdd_IO as it does have an internal pull-up resistor by default, but the datasheet doesn't specify what that resistance is. If you're certain you won't be using SPI, then there is no harm in tying CS directly to Vdd_IO. The pull-up is there for flexibility.

On the evaluation kit of the ILPS22QS (STEVAL-MKI228A), CS is broken out to a connector and not connected to anything further.

eval kit schematic

https://www.st.com/en/evaluation-tools/steval-mki228ka.html#documentation

That being said, it's usually easier to remove components than add them to a design. Adding an external pull-up would be straight forward. If something doesn't work or the device is unreliable, you can add a zero ohm/low value pullup to Vdd_IO, if it does work, don't populate that resistor.

Whenever prototyping and I have a shred of doubt, I always give myself as many options as possible.

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