AN4650 datasheet(40/102 Pages) STMICROELECTRONICS

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Interrupt generation

AN4650

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DocID027415 Rev 1

4.3

Wake-up interrupt

In the LSM6DS3 device the wake-up feature can be implemented using either the slope

filter (see Section 2.6.1 for more details) or the high-pass digital filter, as illustrated in

Figure 2. The filter to be applied can be selected using the SLOPE_FDS bit of the

TAP_CFG register: if this bit is set to 0 (default value), the slope filter is used; if it’s set to 1,

the high-pass digital filter is used.

The wake-up interrupt signal is generated if a certain number of consecutive filtered data

exceed the configured threshold (Figure 12).

The unsigned threshold value is defined using the WK_THS[5:0] bits of the WAKE_UP_THS

1 LSB = (FS_XL)/(26). The threshold is applied to both positive and negative data: for a

wake-up interrupt generation, the module of the filtered data must be bigger than the

threshold.

The duration parameter defines the minimum duration of the wake-up event to be

recognized; its value is set using the WAKE_DUR[1:0] bits of the WAKE_UP_DUR register:

1 LSB corresponds to 1*ODR_XL time, where ODR_XL is the accelerometer output data

rate. It is important to appropriately define the duration parameter to avoid unwanted wake-

up interrupts due to spurious spikes of the input signal.

This interrupt signal can be driven to the two interrupt pins setting to 1 the INT1_WU bit of

the MD1_CFG register or the INT2_WU bit of the MD2_CFG register; it can also be checked

by reading the WU_IA bit of the WAKE_UP_SRC register. The X_WU, Y_WU, Z_WU bits of

the WAKE_UP_SRC register indicate which axis has triggered the wake-up event.

If latch mode is disabled (LIR bit of TAP_CFG is set to 0), the interrupt signal is

automatically reset when the filtered data falls below the threshold. If latch mode is enabled

and the wake-up interrupt signal is driven to the interrupt pins, once a wake-up event has

occurred and the interrupt pin is asserted, it must be reset by reading the WAKE_UP_SRC

pins, the latch feature does not take effect.

Figure 12. Wake-up interrupt (using the slope filter)

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