Knowledge Base Article
Answer: The I2C Clock parameter specifies the required clock speed at which to run the I2C interface. Three clock rates are available:
The 400 kHz I2C speed is only possible if the IMO (SysClk) is at 24 MHz. The maximum communication speed of the I2C bus does not depend on the voltage setting. It is dependent on the SysClk setting. So, if the SysClk is set to 24 MHz in the global resources, you can run the I2C at a maximum speed of 400 kHz.
The clock speed selection in an I2C user module assumes that the SysClk is 24 MHz. If the Sysclk is set to SLIMO mode (6 MHz SysClk) in the global resources, the I2C speed set in the user module parameter will also scale down accordingly. For example, if SysClk is 6 MHz, the possible clock speeds are 12.5K, 25K, and 100K. SysClk is separate from the CPU clock.