LIS2DS12 datasheet(29/68 Pages) STMICROELECTRONICS

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LIS2DS12

Digital main blocks

5.4.6

Module-to-FIFO

When the MODULE_TO_FIFO bit in the FIFO_CTRL (25h) register is set to '1', the 14-bit

magnitude of the vector of the current axes is sent as FIFO input instead of axes data. X-, Y-

and Z-axis data are replaced with 3 times the adjacent data generated by the module

routine, as shown in Figure 11, so a row of FIFO is written every 3 axes data ready.

The module routine must be previously enabled by writing to the FUNC_CTRL (3Fh)

The LIS2DS12 calculates the vector sum of the acceleration of the X-, Y-, Z-axis using the

following formula:

module (14-bit) = Sqrt(x2+y2+z2)

The implementation is based on an approximation of this formula (error below noise level).

If this calculation is used in the application, the FIFO must be increased by 3 since only this

one value is stored in FIFO instead.

Please note that a 14-bit value is stored in FIFO when an 8-bit value is available in each

sample in register Module_8bit (0Ch) (MSBs of original 14-bit value).

Figure 11. Module-to-FIFO mode example

5.5

Embedded functions

The LIS2DS12 embeds internal logic able to implement the following functions:

 Step detector

 Step counter

 Significant motion

 Sensor hub

 Tilt

Pedometer, significant motion, sensor hub, and tilt functions can work in parallel according

to Table 14. Step detector, step counter, tilt function, and significant motion function work at

25 Hz, so the user can configure ODR at 25 Hz or higher.

Table 14. ODR function settings

Sensor hub

Pedometer

Tilt function

Event recognition

ODR

 1600 Hz

ODR < 1600 Hz

ODR 25-50 Hz

ODR 12.5 Hz

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