BMA253
Data sheet
Page 42
4.7.11 No-motion / slow motion detection
The slow-motion/no-motion interrupt engine can be configured in two modes.
In slow-motion mode an interrupt is triggered when the measured slope of at least one enabled
axis exceeds the programmable slope threshold for a programmable number of samples.
Hence the engine behaves similar to the any-motion interrupt, but with a different set of
parameters. In order to suppress false triggers, the interrupt is only generated (cleared) if a
certain number N of consecutive slope data points is larger (smaller) than the slope threshold
given by (0x27) slo_no_mot_dur<1:0>. The number is N = (0x27) slo_no_mot_dur<1:0> + 1.
In no-motion mode an interrupt is generated if the slope on all selected axes remains smaller
than a programmable threshold for a programmable delay time. Figure 11 shows the timing
diagram for the no-motion interrupt. The scaling of the threshold value is identical to that of the
slow-motion interrupt. However, in no-motion mode register (0x27) slo_no_mot_dur defines the
delay time before the no-motion interrupt is triggered. Table 19 lists the delay times adjustable
with register (0x27) slo_no_mot_dur. The timer tick period is 1 second. Hence using short delay
times can result in considerable timing uncertainty.
If bit (0x18) slo_no_mot_sel is set to ‘1’ (‘0’) the no-motion/slow-motion interrupt engine is
configured in the no-motion (slow-motion) mode. Common to both modes, the engine monitors
the slopes of the axes that have been enabled with bits (0x18) slo_no_mot_en_x, (0x18)
slo_no_mot_en_y, and (0x18) slo_no_mot_en_z for the x-axis, y-axis and z-axis, respectively.
The measured slope values are continuously compared against the threshold value defined in
register (0x29) slo_no_mot_th. The scaling is such that 1 LSB of (0x29) slo_no_mot_th
corresponds to 3.91 mg in 2g-range (7.81 mg in 4g-range, 15.6 mg in 8g-range and 31.3 mg in
16g-range). Therefore the maximum value is 996 mg in 2g-range (1.99g in 4g-range, 3.98g in
8g-range and 7.97g in 16g-range). The time difference between the successive acceleration
samples depends on the selected bandwidth and equates to 1/(2 * bw).
Table 19: No-motion time-out periods
(0x27)
slo_no_mot_dur
Delay
time
(0x27)
slo_no_mot_dur
Delay
time
(0x27)
slo_no_mot_dur
Delay
Time
0
1
1 s
2 s
16
17
18
19
20
21
40 s
48 s
56 s
64 s.
72 s
80 s
32
33
34
...
88 s
96 s
104 s
...
2
3 s
...
14
15
...
15 s
16 s
62
63
328 s
336 s
Note: slo_no_mot_dur values 22 to 31 are not specified
BST-BMA253-DS000-01 | Revision 1.0 | August 2015
Bosch Sensortec
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Note: Specifications within this document are subject to change without notice.
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