Specifications

BMA180
Preliminary data sheet
Bosch Sensortec
Rev. 1.0 Page 37 / - proprietary information - 06 March 2009
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Specifications within this document are preliminary and subject to change without notice. Document is not intended for publication.
• low_filt: evaluation if interrupt generation is done with filtered (low_filt = “1”) or
unfiltered (low_filt = “0”) acceleration signal.
• low_dur: low threshold duration and
• ff_cd_r : free_fall_counter_down_register are used for debouncing low-g criteria.
Remarks: - The thresholds codes are compared with the 8 MSB bits of acceleration value
(in absolute value), the low threshold level can thus be selected anywhere in
the full scale range.
- The sign of the acceleration, which has initiated the interrupt signal, is stored in
the flag bit low_sign_int_* (see 7.12.8), only if the corresponding enable
bit low_int_* is set.
7.9.4.3 Low-g interrupt: algorithm
In figure 6 an example is given to explain functionality of the configuration settings and the
algorithm behind the calculation of the interrupt generation.
low_th
low_th + 32*low_hy
acceleration
low G interrupt
counter value
low_dur
INT (not latched here)
ff_cd_r = 10
Count down with double speed
Figure 6: example of free-fall detection debouncing
with use of low_th, low_hy, low_dur and ff_cd_r settings
When acceleration signal is passing low_th value, low_th_criteria becomes active and counter
ff_cd_r is incremented by 1 N
COUNT
. (Ncount = 1 LSB/(5xTupdate) = 1 LSB/2.085ms in low