I2C rise and falltime setting

Sebastian33 · ‎2025-11-27

We have a board with a stm32u5. were VDDIO are connected to 1.8 V and the I2C bus have pullup to 3.0 V. Some I2C devices uses 3.0 V logic levels and som 1.8 V.

Between which voltage levels shall i measure the rise and falltime that i enter in cubemx.

30%->70% of 1.8 V or 3.0 V .

We have possibility to turn off and on some devices on the bus that changes the rise and falltime on the bus. Shall then the longer or shorter rise/falltimes be used?

Andrew Neil · ‎2025-11-27

@Sebastian33 wrote:
the I2C bus have pullup to 3.0 V. Some I2C devices uses 3.0 V logic levels and som 1.8 V. ?

Surely, that cannot work ?

The 1.8V devices need to be on a 1.8V bus ?

In any I2C bus, the master needs to be configured to a setting that will work for all slaves on the bus.

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.