BMA255 datasheet(37/119 Pages) BOSCH

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BMA255

Data sheet

Page 37

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.

4.7.7.1 Orientation blocking

The change of the (0x0C) orient value and – as a consequence – the generation of the interrupt

can be blocked according to conditions selected by setting the value of the (0x2C)

orient_blocking bits as described by Table 17.

Table 17: Blocking conditions for orientation recognition

(0x2C)

orient_blocking

Conditions

00b

no blocking

01b

theta blocking

acceleration in any axis > 1.5g

10b

theta blocking

acceleration slope in any axis > 0.2 g

acceleration in any axis > 1.5g

11b

theta blocking

acceleration slope in any axis > 0.4 g

acceleration in any axis > 1.5g and value of orient is

not stable for at least 100 ms

The theta blocking is defined by the following inequality:

tan

theta

blocking





The parameter blocking_theta of the above given equation stands for the contents of the (0x2D)

orient_theta bits. It is possible to define a blocking angle between 0° and 44.8°. The internal

blocking algorithm saturates the acceleration values before further processing. As a

consequence, the blocking angles are strictly valid only for a device at rest; they can be

different if the device is moved.

Example:

To get a maximum blocking angle of 19° the parameter blocking_theta is determined in the

following way: (8 * tan(19°) )² = 7.588, therefore, blocking_value = 8dec = 001000b has to be

chosen.

In order to avoid unwanted generation of the orientation interrupt in a nearly flat position (z ~ 0,

sign change due to small movements or noise), a hysteresis of 0.2 g is implemented for the z-

axis, i. e. a after a sign change the interrupt is only generated after |z| > 0.2 g.

4.7.7.2 Up-Down Interrupt Suppression Flag

Per default an orientation interrupt is triggered when any of the bits in register (0x0C) orient

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