AN2335 datasheet(25/40 Pages) STMICROELECTRONICS

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AN2335

Free-Fall and Wake-Up Registers

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AOI bit allows to select between Wake-Up (OR combination of interrupt events) and Free-

Fall (AND combination of interrupt events) detection

LIR defines whether the configured interrupt event has to be latched by the device once it

has happened. The interrupt request is cleared by reading the related source reg

(FF_WU_SRC_1).

XHIE (YHIE, ZHIE) set an interrupt event to occur when the measured acceleration data on

X (Y, Z) channel is higher than the threshold set in FF_WU_THS_1 register.

XLIE (YLIE, ZLIE) set an interrupt event to occur when the measured acceleration data on X

(Y, Z) channel is lower than the threshold set in FF_WU_THS_1 register.

The threshold module which is used by the system to detect any free-fall or inertial wake-up

event is defined by FF_WU_THS_1. The threshold value is expressed over 7 bit as an

unsigned number and X, (Y, Z) high is true when the unsigned acceleration value of the X (Y,

Z) channel is higher than or egual to FF_WU_THS_1. Similarly, X, (Y, Z) low is true when

the unsigned acceleration value of the X (Y, Z) channel is lower than FF_WU_THS_1. Refer

to Figure 11 for more details.

Figure 11.

FF_WU_CFG_1,2 High and Low value

8.3

FF_WU_SRC_1 (31h)

Free-fall and wake-up source register for interrupt 1. Read only register.

+ Full Scale

- Full Scale

0 g level

Threshold module

X (Y, Z) high

X (Y, Z) low

Positive

Negative

acceleration

YHYLXHXL

Interrupt Active. Default value: 0

(0: no interrupt has been generated;

1: one or more interrupt event has been generated)

Z High. Default value: 0

(0: no interrupt; 1: ZH event has occurred)

Z Low. Default value: 0

(0: no interrupt; 1: ZL event has occurred)

Y High. Default value: 0

(0: no interrupt; 1: YH event has occurred)

Y Low. Default value: 0

(0: no interrupt; 1: YL event has occurred)

X High. Default value: 0

(0: no interrupt; 1: XH event has occurred)

X Low. Default value: 0

(0: no interrupt; 1: XL event has occurred)

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