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Configuration Setting Lock

Category: Hardware
Product Number: ADXL355

The Rev B data sheet states that for register 0x2D, bit 0 that: Standby mode. In standby mode, the device is in a low power state, and the temperature and acceleration data paths are not operating. In addition, digital functions, including FIFO pointers,  reset. Changes to the configuration setting of the device must be made when standby = 1. An exception is a high-pass filter that can be changed when the device is operating. Elsewhere it states that other settings, like self-test and reset registers can be changed. The data sheet is ambiguous when it comes to WHICH registers are locked in measurement mode. 

The data sheet does not clearly define which registers are considered "configuration" registers that enter the locked state when in the measurement mode. In particular, are the Range settings [0:1] in register 0x2C locked when in in the measurement mode?

Consider adding a column to Table 15 to define which registers are locked in Measurement mode. This would also help highlight this function and the potential issues it might create if the written notes are missed.

  • Sense I did not get a response to my original question I did some tests with ADXL355 myself. It appears the range setting is NOT protected from changes when in the measurement mode. A new value can be written to this register and then read back, indicating the new written value has been accepted. It is hard to say what impact this might have on the actual acceleration values that are being read, particularly those that might be in process at the time of the change. It is unclear how the range setting is implemented inside the ADXL. The range setting could simply shift the output data of the ADC or it could be changing the gain of the input of the ADC. These have different affects on the acceleration output value if changed during acquisition.

    This ability to change the range setting seems to be in conflict with the datasheet that does not mention this as a changeable value when in the measurement mode of operations. It is also not clear if the range of the device actually changes under these conditions.

    Again, please consider updating the datasheet to clarify locked values in the measurement mode of operations. Also please clarify the affect of range changes while the ADXL is acquiring a new sample.