Interrupt generation

AN2847

22/31

Doc ID 15136 Rev 2

The ZHIE, ZLIE, YHIE, YLIE, XHIE and HLIE bits of the INTx_CFG register select on which

axis the interrupt decision must be performed, and in which direction the threshold must be

exceeded to generate the interrupt request.

Figure 8.

Free-fall, wake-up interrupt generator

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

events is defined by the INTx_THS registers. The threshold value is expressed over 7 bits as

an unsigned number and is symmetrical around the zero-g level. XH (YH, ZH) is true when

the unsigned acceleration value of the X (Y, Z) channel is higher than INTx_THS. Similarly,

XL, (YL, ZL) low is true when the unsigned acceleration value of the X (Y, Z) channel is

lower than INTx_THS. Refer to

Figure 9 for additional details.

THS reg

|b|>a?

|b|<a?

Accel_X

XHE

XLE

WU

FF

0

1

INTx_CFG(AOI)

|b|>a?

|b|<a?

YHE

YLE

|b|>a?

|b|<a?

ZHE

ZLE

Accel_Y

Accel_Z

0

1

INTx_CFG(AOI)

1

0

0

1

a

b

a

b