MMA8653FC datasheet(33/56 Pages) FREESCALE

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MMA8653FC

Sensors

Freescale Semiconductor, Inc.

6.6

Motion and Freefall embedded function registers

The freefall/motion function can be configured in either Freefall or Motion Detection mode via the OAE configuration bit (0x15:

FF_MTG_CFG, bit 6). The freefall/motion detection block can be disabled by setting all three bits ZEFE, YEFE, and XEFE to zero.

Depending on the register bits ELE (0x15: FF_MTG_CFG, bit 7) and OAE (0x15: FF_MTG_CFG, bit 6), each of the freefall and

motion detection block can operate in four different modes:

6.6.1

Motion and freefall mode

6.6.1.1

Mode 1: Freefall Detection with ELE = 0, OAE = 0

In this mode, the EA bit (0x16: FF_MTG_SRC, bit 7) indicates a freefall event after the debounce counter is complete.

The ZEFE, YEFE, and XEFE control bits determine which axes are considered for the freefall detection. Once the EA

bit is set, and DBCNTM = 0, the EA bit can get cleared only after the delay specified by FF_MT_COUNT. This is

because the counter is in decrement mode. If DBCNTM = 1, the EA bit is cleared as soon as the freefall condition

disappears, and will not be set again before the delay specified by FF_MT_COUNT has passed. Reading the

FF_MT_SRC register does not clear the EA bit. The event flags (0x16) ZHE, ZHP, YHE, YHP, XHE, and XHP reflect

the motion detection status (i.e. high g event) without any debouncing, provided that the corresponding bits ZEFE,

YEFE, and/or XEFE are set.

6.6.1.2

Mode 2: Freefall Detection with ELE = 1, OAE = 0

In this mode, the EA event bit indicates a freefall event after the debounce counter. Once the debounce counter

reaches the time value for the set threshold, the EA bit is set, and remains set until the FF_MT_SRC register is read.

When the FF_MT_SRC register is read, the EA bit and the debounce counter are cleared and a new event can only be

generated after the delay specified by FF_MT_CNT. The ZEFE, YEFE, and XEFE control bits determine which axes

are considered for the freefall detection. While EA = 0, the event flags ZHE, ZHP, YHE, YHP, XHE, and XHP reflect the

motion detection status (i.e., high g event) without any debouncing, provided that the corresponding bits ZEFE, YEFE,

and/or XEFE are set. The event flags ZHE, ZHP, YHE, YHP, XHE, and XHP are latched when the EA event bit is set.

The event flags ZHE, ZHP, YHE, YHP, XHE, and XHP will start changing only after the FF_MT_SRC register has been

read.

6.6.1.3

Mode 3: Motion Detection with ELE = 0, OAE = 1

In this mode, the EA bit indicates a motion event after the debounce counter time is reached. The ZEFE, YEFE, and

XEFE control bits determine which axes are taken into consideration for motion detection. Once the EA bit is set, and

DBCNTM = 0, the EA bit can get cleared only after the delay specified by FF_MT_COUNT. If DBCNTM = 1, the EA bit

is cleared as soon as the motion high g condition disappears.

The event flags ZHE, ZHP, YHE, YHP, XHE, and XHP reflect the motion detection status (i.e., high g event) without

any debouncing, provided that the corresponding bits ZEFE, YEFE, and/or XEFE are set. Reading the FF_MT_SRC

does not clear any flags, nor is the debounce counter reset.

6.6.1.4

Mode 4: Motion Detection with ELE = 1, OAE = 1

In this mode, the EA bit indicates a motion event after debouncing. The ZEFE, YEFE, and XEFE control bits determine

which axes are taken into consideration for motion detection. Once the debounce counter reaches the threshold, the

EA bit is set, and remains set until the FF_MT_SRC register is read. When the FF_MT_SRC register is read, all

specified by FF_MT_CNT.

While the bit EA is zero, the event flags ZHE, ZHP, YHE, YHP, XHE, and XHP reflect the motion detection status (i.e.,

high g event) without any debouncing, provided that the corresponding bits ZEFE, YEFE, and/or XEFE are set. When

the EA bit is set, these bits keep their current value until the FF_MT_SRC register is read.

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