ADXL372 - Peak Detection and FIFO triggered mode?

Hi John92783 ,

We have recently updated the datasheet (RevC) to reflect your observation (in pages 21 and 22). FIFO is not needed to record me maximum peak.  

ADXL372 (Rev. C) (analog.com)

I hope this helps, 

Pablo

Hi Pablo,

I was looking at revC when I wrote this question. On pages 21/22 it gives two examples on how to enable 'peak detection'. In both cases, it mentions configuring the FIFO as the first step:

Hence my question. It seems the second example is referring to using the FIFO to store maximum peaks. But in the first example, I'm not sure why step 1 says to config the FIFO. So, can we confirm that the FIFO is definitely not needed in order to store maximum peaks? 

I've configured the sensor for peak detection, and seem to have it look like it's working.
But your point about FIFO not being needed for peak detection, when reading MAXPEAK_x_x register can't be true, surely. Not only does the datasheet say FIFO needs to be configured,
If I set FIFO_CTL to 0, the peak detection triggers, but the values read out are all 0. If I configure the FIFO_CTL for peak detect mode, it triggers, and the values read show some g reading.

In this configuration, Is there a risk that the values read then may be misaligned due to the FIFO read/write pointer collision issue with the ADXL372? I need an absolute answer as our application MUST require the max peak values being on the correct axes. I'm using this peak detection as a workaround for the FIFO bug.

Thanks.

Hi John92783 , 

Are you reading the max peak values directly from the max peak registers? if so, the max peak detection happens in the analog domain and the max peak values are directly stored in the max peaks registers. No FIFO intervention. Please have into account the max peak function limitations, as described in the datasheet. 

We provided a workaround for the FIFO misalignment in the datasheet as well. As long as you follow the recommended routine you should not have any issue. 

Regards, 

Pablo. 

Hi Pdel,

Sorry to revive this thread. I had to work on other stuff in the meantime. Just coming back to this issue.

"the max peak detection happens in the analog domain and the max peak values are directly stored in the max peaks registers."

That's what I thought, after reading the data sheet, but I cannot get any actual values that are not 0 from the peak detection registers, unless I configure 

FIFO_FORMAT to 111 (store peak events) in FIFO_CTL register. Just like I mentioned in previous response.

When I set FIFO_CTL reg to be all 0, the activity interrupt fires, I read max peak registers but all values are 0

When I set FIFO_CTL reg to 0x38 (enable storing of peak events), the same happens, except the values are non-zero.

I'm only reading from the maxpeak registers.

Am I missing something here, or is the FIFO in fact, required somehow for peak detection. Maybe the max peak registers are tied to the FIFO somehow? If you could confirm that for me that would be great.