The ADcmXL3021 datasheet revision 0 seems to have conflicting information regarding the bit settings in AVG_CNT register.
In page 23 table 20 (BASIC OPERATION -> SAMPLE RATE), the following valid settings (1 to 128x decimation factor) are listed:
However, in page 41 table 89 (USER REGISTER DETAILS -> AVG_CNT), the following settings are listed as valid:
Which one is correct? I haven't been able to try it myself against a known frequency, but based on a quick measurement the values in first table seem to produce more realistic output.
On a somewhat related note, in page 35 (USER REGISTER DETAILS -> X_BUF), the following formula is presented for transforming raw FFT buffer values to mg:
Does Number of FFT Averages refer to AVG_CNT or FFT_AVG1/FFT_AVG2 setting? Both are referred to as "FFT averages" at some point in the data sheet. I believe it should be AVG_CNT because I can't see how the actual averaging across FFT measurements could affect the output data format, however I don't want to count on it.
Q1: Table 20 is has the correct SPS calculation.
Q2: It refers to FFT_AVG. It is just how the data is structured in the registers.