MMA8452Q

Sensors

30

Freescale Semiconductor, Inc.

6.4

Transient (HPF) Acceleration Detection

For more information on the uses of the transient function please review 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