Interrupt generation

AN2989

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Doc ID 15761 Rev 1

Figure 11.

Free-fall interrupt

This paragraph provides the fundamentals for using the free-fall detection feature. In

particular, the software routine which configures the device to detect and signal free-fall

events is as follows:

The code sample exploits a threshold set at 350 mg for free-fall recognition and the event is

notified by the hardware signal INT1. At step 5, the INT1_DURATION register is configured

to ignore events that are shorter than 3/DR = 3/100 ~= 30 ms in order to avoid false

detections.

Once the free-fall event has occurred, a read at the INT1_SRC register clears the request

and the device is ready to recognize other events.

5.6

6D direction

The LIS331DLM features an advanced capability to detect the orientation of the device in

space. The 6D direction function can be enabled through the AOI and 6D bits of the

INT1_CFG register (Table 3). When configured for the 6D function, the ZH, ZL, YH, YL, XH,

1

write 2Fh into CTRL_REG1

// Turn-on the sensor, enable X, Y and Z

// ODR = 100 Hz

2

write 00h into CTRL_REG2

// High-pass filter disabled

3

write 04h into CTRL_REG3

// Latched interrupt on INT1

4

write 16h into INT1_THS

// Set free-fall threshold = 350 mg

5

write 03h into INT1_DURATION

// Set minimum event duration

6

write 95h into INT1_CFG

// Configure free-fall recognition

7

poll INT1 pad; if INT1 = 0 then goto 8

// Poll INT1 pin waiting for the free-fall event

8

(Free-fall event has occurred; insert your

code here)

// Event handling

9

read INT1_SRC register

// Clear interrupt request

10

goto 7