Tips on connecting two of FRDM-KL02Z I2C

Document created by Fang Li Employee on Sep 28, 2015
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This sample is to use two FRDM-KL02Z to testing the I2C.  By working at 400KHz baud rate, some customer may found the I2C_SDA will generating a dig when failing edge of the I2C_CLK.  Actually it should related with I2C port layout and the question is why this happen and how to get rid of the dig?

 

The truth is I2C pins are open drain, so no one actually drives a high value. The high value is only there because of a pullup resistor on the lines. For the case to connect two of FRDM-KL02Z using the I2C0_SCL and I2C0_SDA lines that are available on J7, these lines are also used for connecting to the inertial sensor that is on the board, and there are 4.7K pullups on both lines. Problem is that there are 4.7K pullups on the lines on both boards, so the pullups are weaker than intended. So customer should remove the pullup resistors from one of the two boards that should help. We even recommend customer might need to replace the 4.7K pullups with an even stronger pullup though when they have more devices on the I2C bus that are all adding loading.

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