Am I correct that table 19 and table 20 on page 16 of the Data Sheet rev B is not adding up?

Default = 0x0108 in Table 19

Default = 0x0101 in Table 20

are they not the same?

In the previous text FFT_AVG(8:0) is likely to be 7:0?

"to set the number of FFT averages to 16 for the SR2 sample rate option and 1024 for the S3"

is 1024 a accepted number?

I am just trying to have it make sense or am I confused on a higher level?

Olov

Hello Olov,

After reviewing this section of the datasheet and our internal design documentation, I realized that I was mistaken in my previous feedback and that we definitely needed to revise this section of the datasheet. As embarrassing as this is, let me detail where I was wrong, for clarity and then offer the updated datasheet section for your feedback.

EXAMPLE: set FFT_AVG2[7:0] = 0x10 (DIN = 0x8E10) to configure the device to use 16 FFT individual FFT results in a single record for the SR2 setting.

Here is the updated datasheet section, which is currently in draft state. This will likely be submitted for revision in approximately 2-3 weeks, so we can completely review the rest of the datasheet.

## FFT

The FFT function translates a 512-sample time record into a 256-point spectral record that provides magnitude vs. frequency data. Each FFT result loads into an accumulator stage that averages multiple FFT results for the FFT record.

## FFT Averaging

FFT_AVG1 (Table 19) and FFT_AVG2 (Table 20) contain user-configurable settings for the total number of FFT results in each record. Each byte contains a binary number that sets the number of averages for a particular sample rate setting (SR0-SR3, per AVG_CNT register, See Table 11). For example, set FFT_AVG1[15:8] = 0x0B (DIN = 0x8D0B) to set the total number of averages for the SR1 setting to 11. The default setting for the SR0 sample rate cause an average of 8 FFT results for one FFT record. The default settings for SR1, SR2 and SR3 cause each FFT to contain only one FFT result (no averaging).

Table 19. FFT_AVG1 (Base Address = 0x0C), Read/WriteBitsDescription (Default = 0x0108)[15:8]

Number of FFT results (N

_{F}in Figure 14) in a FFT record, for sample rate SR1. range = 1 to 255, binary format[7:0]

Number of FFT results (N

_{F}in Figure 14) in a FFT record, for sample rate SR0. range = 1 to 255, binary formatTable 20. FFT_AVG2 (Base Address = 0x0E), Read/Write

BitsDescription (Default = 0x0101)[15:8]

Number of FFT results (N

_{F}in Figure 14) in a FFT record, for sample rate SR3. range = 1 to 255, binary format[7:0]

Number of FFT results (N

_{F}in Figure 14) in a FFT record, for sample rate SR2. range = 1 to 255, binary formatI hope that helps clear the confusion. If you have any questions, please let me know. I am very sorry about the confusion I created. I was simply reading the wrong part of our internal software specification and didn't realize it until I set it down for a few days and then revisited this topic.

Very best,

NevadaMark