Datasheet

BMA250E
Data sheet
Page 39
BST-BMA250E-DS004-06 | Revision 1.3 | April 2015 Bosch Sensortec
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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
8
1
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:
















16
_
1024
_
1flat_theta
8
1
atan
,
hyflathyflat
llhyst
The flat position is reset if the angle exceeds the following threshold:
















16
_
1024
_
1flat_theta
8
1
atan
,
hyflathyflat
ulhyst
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
0
01b
512 ms
10b
1024 ms
11b
2048 ms