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ADXL375 App Note AN-1266 is missing an essential step in the write sequence

Question asked by SpiSpy on Nov 9, 2017
Latest reply on Nov 9, 2017 by NevadaMark

In the app note "Autonomous Shock Event Monitoring" an explicit sequence of writes is provided to test the shock detect functionality. This is a good example, but an essential write is missing that is difficult to notice and debug. As a result the ADXL375 reports incorrect/saturated data if you follow the example. The missing write is to the DATA_FORMAT (0x31) register. The reset value of that register is invalid (all zero).


This cost me a lot of time because I thought I had made a mistake in my interpretation/scaling of the data from the device.


It is not surprising that even ADI engineers make this mistake. The datasheet is very unclear on the importance of the reserved bits in the DATA_FORMAT register. It does not even mention them except as nameless 1s in the register table. The datasheet should be much more explicit about the need to write these bits and how essential they are for correct function across the full operational range. (Even better, they should be fixed in the hardware since they have no function other than as a source of bugs...)