BMA255 datasheet(39/119 Pages) BOSCH

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BMA255

Data sheet

Page 39

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.

4.7.8 Flat detection

The flat detection feature gives information about the orientation of the devices´ z-axis relative

to the g-vector, i. e. it recognizes whether the device is in a flat position or not.

The flat angle

 is adjustable by (0x2E) flat_theta from 0° to 44.8°. The flat angle can be set

according to following formula:

















flat_theta

atan

A hysteresis of the flat detection can be enabled by (0x2F) flat_hy bits. In this case the flat

position is set if the angle drops below following threshold:

























 







1024

flat_theta

atan

flat

hyst

The flat position is reset if the angle exceeds the following threshold:

























 







1024

flat_theta

atan

flat

hyst

The flat interrupt is enabled (disabled) by writing ´1´ (´0´) to bit (0x16) flat_en. The flat value is

stored in the (0x0C) flat bit if the interrupt is enabled. This value is ´1´ if the device is in the flat

position, it is ´0´ otherwise. The flat interrupt is generated if the flat value has changed and the

new value is stable for at least the time given by the (0x2F) flat_hold_time bits. A flat interrupt

may be also generated if the flat interrupt is enabled. The actual status of the interrupt is stored

in the (0x09) flat_int bit. The flat orientation of the sensor can always be determined from

reading the (0x0C) flat bit after interrupt generation. If unlatched interrupt mode is used, the

(0x09) flat_int value and hence the interrupt is automatically cleared after one sample period. If

temporary or latched interrupt mode is used, the (0x09) flat_int value is kept fixed until the latch

time expires or the interrupt is reset.

The meaning of the (0x2F) flat_hold_time bits can be seen from Table 18.

Table 18: Meaning of flat_hold_time

(0x2F)

flat_hold_time

Time

00b

01b

512 ms

10b

1024 ms

11b

2048 ms

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