Data Sheet

MMA8452Q
Sensors
30 Freescale Semiconductor, Inc.
6.4 Transient (HPF) Acceleration Detection
For more information on the uses of the transient function please review Freescale application note, AN4071. This function is
similar to the motion detection except that high-pass filtered data is compared. There is an option to disable the high-pass filter
through the function. In this case the behavior is the same as the motion detection. This allows for the device to have 2 motion
detection functions.
0x1D: Transient_CFG Register
The transient detection mechanism can be configured to raise an interrupt when the magnitude of the high-pass filtered
acceleration threshold is exceeded. The TRANSIENT_CFG register is used to enable the transient interrupt generation
mechanism for the 3 axes (X, Y, Z) of acceleration. There is also an option to bypass the high-pass filter. When the high-pass
filter is bypassed, the function behaves similar to the motion detection.
0x1E: TRANSIENT_SRC Register
The Transient Source register provides the status of the enabled axes and the polarity (directional) information. When this
register is read it clears the interrupt for the transient detection. When new events arrive while EA = 1, additional *TRANSE bits
may get set, and the corresponding *_Trans_Pol flag become updated. However, no *TRANSE bit may get cleared before the
TRANSIENT_SRC register is read.
When the EA bit gets set while ELE = 1, all other status bits get frozen at their current state. By reading the TRANSIENT_SRC
register, all bits get cleared.
0x1D: TRANSIENT_CFG Register (Read/Write)
Bit
7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
0 0 0 ELE ZTEFE YTEFE XTEFE HPF_BYP
Table 31. TRANSIENT_CFG Description
ELE
Transient event flags are latched into the TRANSIENT_SRC register. Reading of the TRANSIENT_SRC register clears the event
flag. Default value: 0.
0: Event flag latch disabled; 1: Event flag latch enabled
ZTEFE
Event flag enable on Z transient acceleration greater than transient threshold event. Default value: 0.
0: Event detection disabled; 1: Raise event flag on measured acceleration delta value greater than transient threshold.
YTEFE
Event flag enable on Y transient acceleration greater than transient threshold event. Default value: 0.
0: Event detection disabled; 1: Raise event flag on measured acceleration delta value greater than transient threshold.
XTEFE
Event flag enable on X transient acceleration greater than transient threshold event. Default value: 0.
0: Event detection disabled; 1: Raise event flag on measured acceleration delta value greater than transient threshold.
HPF_BYP
Bypass High-Pass filter Default value: 0.
0: Data to transient acceleration detection block is through HPF 1: Data to transient acceleration detection block is NOT through
HPF (similar to motion detection function)
0x1E: TRANSIENT_SRC Register (Read Only)
Bit
7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
0 EA ZTRANSE Z_Trans_Pol YTRANSE Y_Trans_Pol XTRANSE X_Trans_Pol
Table 32. TRANSIENT_SRC Description
EA
Event Active Flag. Default value: 0.
0: no event flag has been asserted; 1: one or more event flag has been asserted.
ZTRANSE
Z transient event. Default value: 0.
0: no interrupt, 1: Z Transient acceleration greater than the value of TRANSIENT_THS event has occurred
Z_Trans_Pol
Polarity of Z Transient Event that triggered interrupt. Default value: 0.
0: Z event was Positive g, 1: Z event was Negative g
YTRANSE
Y transient event. Default value: 0.
0: no interrupt, 1: Y Transient acceleration greater than the value of TRANSIENT_THS event has occurred
Y_Trans_Pol
Polarity of Y Transient Event that triggered interrupt. Default value: 0.
0: Y event was Positive g, 1: Y event was Negative g
XTRANSE
X transient event. Default value: 0.
0: no interrupt, 1: X Transient acceleration greater than the value of TRANSIENT_THS event has occurred
X_Trans_Pol
Polarity of X Transient Event that triggered interrupt. Default value: 0.
0: X event was Positive g, 1: X event was Negative g