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STM32L011 I2C timing calculation

Question asked by Nick McKendree on Feb 15, 2018
Latest reply on Feb 15, 2018 by Grant Stocker

Can anyone help to explain the method to calculate the I2C timing register?


I am trying to come up with a value for 400KHz. I2C1 clock is from HSI16 which also has the /div4 enabled.

I am very confused by the set up times such as tSU;DAT.


The issue is that I am not reading the bytes correctly, which corresponds with the device errata

Wrong data sampling when data set-up time (tSU;DAT) is smaller than one I2CCLK period Description The I2C bus specification and user manual specifies a minimum data set-up time (tSU;DAT) at:

• 250 ns in Standard-mode,

• 100 ns in Fast-mode,

• 50 ns in Fast-mode Plus.

The I2C SDA line is not correctly sampled when tSU;DAT is smaller than one I2CCLK (I2C clock) period: the previous SDA value is sampled instead of the current one. This can result in a wrong slave address reception, a wrong received data byte, or a wrong received acknowledge bit. DocID028471 Rev 4 11/17 STM32L011x3/4 STM32L011x3/4 silicon limitations 16 Workaround Increase the I2CCLK frequency to get I2CCLK period smaller than the transmitter minimum data set-up time. Or, if it is possible, increase the transmitter minimum data set-up time.

I tried to use the value from STM32CubeMX and it did not help.


Processor: STM32L011K4