Datasheet
MMA8451Q
Sensors
36 Freescale Semiconductor, Inc.
0x1F: TRANSIENT_THS Register
The Transient Threshold register sets the threshold limit for the detection of the transient acceleration. The value in the
TRANSIENT_THS register corresponds to a g value which is compared against the values of High-Pass Filtered Data. If the High-
Pass Filtered acceleration value exceeds the threshold limit, an event flag is raised and the interrupt is generated if enabled.
The threshold THS[6:0] is a 7-bit unsigned number, 0.063g/LSB. The maximum threshold is 8g. Even if the part is set to full
scale at 2g or 4g this function will still operate up to 8g. If the Low Noise bit is set in Register 0x2A, the maximum threshold to be
reached is 4g.
0x20: TRANSIENT_COUNT
The TRANSIENT_COUNT sets the minimum number of debounce counts continuously matching the condition where the
unsigned value of high-pass filtered data is greater than the user specified value of TRANSIENT_THS.
The time step for the transient detection debounce counter is set by the value of the system ODR and the Oversampling mode.
0x1F: TRANSIENT_THS Register (Read/Write)
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
DBCNTM THS6 THS5 THS4 THS3 THS2 THS1 THS0
Table 41. TRANSIENT_THS Description
DBCNTM Debounce counter mode selection. Default value: 0. 0: increments or decrements debounce; 1: increments or clears counter.
THS[6:0] Transient Threshold: Default value: 000_0000.
0x20: TRANSIENT_COUNT Register (Read/Write)
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
D7 D6 D5 D4 D3 D2 D1 D0
Table 42. TRANSIENT_COUNT Description
D[7:0] Count value. Default
value:
0000_0000
.
Table 43. TRANSIENT_COUNT Relationship with the ODR
ODR (Hz)
Max Time Range (s) Time Step (ms)
Normal LPLN HighRes LP Normal LPLN HighRes LP
800 0.319 0.319 0.319 0.319 1.25 1.25 1.25 1.25
400 0.638 0.638 0.638 0.638 2.5 2.5 2.5 2.5
200 1.28 1.28 0.638 1.28 5 5 2.5 5
100 2.55 2.55 0.638 2.55 10 10 2.5 10
50 5.1 5.1 0.638 5.1 20 20 2.5 20
12.5 5.1 20.4 0.638 20.4 20 80 2.5 80
6.25 5.1 20.4 0.638 40.8 20 80 2.5 160
1.56 5.1 20.4 0.638 40.8 20 80 2.5 160