BMA255 datasheet(34/119 Pages) BOSCH

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BMA255

Data sheet

Page 34

BST-BMA255-DS004-05 | Revision 1.2 | August 2014

Bosch Sensortec

third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.

Note: Specifications within this document are subject to change without notice.

4.7.7 Orientation recognition

The orientation recognition feature informs on an orientation change of the sensor with respect

to the gravitational field vector ‘g’. The measured acceleration vector components with respect

to the gravitational field are defined as shown in figure 9.

Figure 9: Definition of vector components

Therefore, the magnitudes of the acceleration vectors are calculated as follows:

acc_x = 1g x sin

 x cos

acc_y = −1g x sin

 x sin

acc_z = 1g x cos



acc_y/acc_x = −tan



Depending on the magnitudes of the acceleration vectors the orientation of the device in the

space is determined and stored in the three (0x0C) orient bits. These bits may not be reset in

the sleep phase of low-power mode. There are three orientation calculation modes with different

thresholds for switching between different orientations: symmetrical, high-asymmetrical, and

low-asymmetrical. The mode is selected by setting the (0x2C) orient_mode bits as given in

Table 13.

Table 13: Orientation mode settings

(0x2C)

orient_mode

Orientation Mode

00b

symmetrical

01b

high-asymmetrical

10b

low-asymmetrical

11b

symmetrical

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