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MMA8451Q

0x15 FF_MT_CFG Freefall/Motion Configuration Register

This is the Freefall/Motion configuration register for setting up the conditions of the freefall or motion function.

OAE bit allows the selection between Motion (logical OR combination) and Freefall (logical AND combination) detection.

ELE denotes whether the enabled event flag will to be latched in the FF_MT_SRC register or the event flag status in the

FF_MT_SRC will indicate the real-time status of the event. If ELE bit is set to a logic ‘1’, then the event flags are frozen when the

EA bit gets set, and are cleared by reading the FF_MT_SRC source register.

ZHFE, YEFE, XEFE enable the detection of a motion or freefall event when the measured acceleration data on X, Y, Z channel

is beyond the threshold set in FF_MT_THS register. If the ELE bit is set to logic ‘1’ in the FF_MT_CFG register new event flags

are blocked from updating the FF_MT_SRC register.

FF_MT_THS is the threshold register used to detect freefall motion events. The unsigned 7-bit FF_MT_THS threshold register

holds the threshold for the freefall detection where the magnitude of the X and Y and Z acceleration values is lower or equal than

the threshold value. Conversely, the FF_MT_THS also holds the threshold for the motion detection where the magnitude of the

X or Y or Z acceleration value is higher than the threshold value.

Figure 13. FF_MT_CFG High and Low g Level

0x16 FF_MT_SRC Freefall/Motion Source Register

0x15 FF_MT_CFG Register (Read/Write)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

ELE

OAE

ZEFE

YEFE

XEFE

—

Table 33. FF_MT_CFG Description

ELE

Event Latch Enable: Event flags are latched into FF_MT_SRC register. Reading of the FF_MT_SRC register clears the event

flag EA and all FF_MT_SRC bits. Default value: 0.

0: Event flag latch disabled; 1: event flag latch enabled

OAE

Motion detect / Freefall detect flag selection. Default value: 0. (Freefall Flag)

0: Freefall Flag (Logical AND combination)

1: Motion Flag (Logical OR combination)

ZEFE

Event flag enable on Z Default value: 0.

0: event detection disabled; 1: raise event flag on measured acceleration value beyond preset threshold

YEFE

Event flag enable on Y event. Default value: 0.

0: Event detection disabled; 1: raise event flag on measured acceleration value beyond preset threshold

XEFE

Event flag enable on X event. Default value: 0.

0: event detection disabled; 1: raise event flag on measured acceleration value beyond preset threshold

0x16: FF_MT_SRC Freefall and Motion Source Register (Read Only)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

—

ZHE

ZHP

YHE

YHP

XHE

XHP

+8g

High g + Threshold (Motion)

Low g Threshold (Freefall)

High g - Threshold (Motion)

-8g

X, Y, Z High g Region

X, Y, Z Low g Region

Negative

Positive

Acceleration

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