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SPI Bus Corruption even if the sensor is deactivated

Thread Summary

The user encountered bus contention when attempting to access a Serial Flash SPI slave while the ADXL357 was deactivated (CS high). The support engineer suggested probing the SCLK line for ringing and adding a 100Ohm resistor between the controller and ADXL357 to resolve the issue.
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Category: Hardware
Product Number: ADXL357

Hello, 

We are using ADXL357 alongside another SPI slave (Serial Flash). 
Sensor can be accessed with no issues. However, if the ADXL is deactivated (CS manually high), the 
other SPI slave can not be accessed, indicating a bus contention !.
If the ADXL is taken off completely, the other SPI slave works as expected. 
Further test showed that if the CS is manually deactivated (logic high) and the SCK pin of the ADXL is removed from
the bus, the other SPI slave works too. 
Our firmware test is very simple. It only reads IDs of both SPI slaves (after the problem has been narrowed down). 
We expect the sensor to be fully deactivated if the CS is logic high. 
We also know from the user manual that "The interface affectively autodetects the format being used, requiring no configuration control to select the format."
So, we first accessed the ADXL to read its ID (so that the internal logic knows this is SPI communication). 
This is urgent matter and we need to know if this can ever happen with that sensor? 

  • Hi  

    I wonder if there is sort of inductance on the path or impedance mismatch that could result in ringing on the SCLK line that is affecting the other device ability to communicate? If you can probe the SCLK will help to validate/refute this idea. 

    Also, can you please check if the issue persists of you add a ~100Ohm resistor on the path between the SCLK of the controller and the ADXL357? 

    Thanks, 

    Pablo.