LPS22DF datasheet(32/54 Pages) STMICROELECTRONICS

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Figure 22. "Threshold-based" interrupt event

P_DIFF_IN

Negative

Threshold positive value

Threshold negative value

Positive

To enable the AUTOZERO mode, the AUTOZERO bit must be set to '1' and then the measured pressure value

is used as the reference and stored in the register REF_P (REF_P_L (16h), REF_P_H (17h)). From this point

on, the output pressure value (PRESS_OUT_XL (28h), PRESS_OUT_L (29h), PRESS_OUT_H (2Ah)) is updated

with the difference between the measured pressure and REF_P.

•

P_DIFF_IN = measured pressure - REF_P

•

PRESS_OUT = measured pressure - REF_P

After the first conversion, the AUTOZERO bit is automatically set back to '0'. In order to return back to normal

mode, the RESET_AZ bit in the INTERRUPT_CFG (0Bh) register has to be set to '1'. This also resets the content

of the REF_P registers to 0.

AUTOREFP mode allows using the pressure differential for the generation of the interrupt keeping the output

pressure registers PRESS_OUT (PRESS_OUT_XL (28h), PRESS_OUT_L (29h), PRESS_OUT_H (2Ah)) without

comparing REF_P. If the AUTOREFP bit is set to '1', the measured output pressure is used as the reference in the

•

P_DIFF_IN = measured pressure - REF_P

The output registers PRESS_OUT (28h, 29h and 2Ah) are not changed by REF_P and shows as follows.

•

PRESS_OUT = measured pressure

After the first conversion, the AUTOREFP bit is automatically set to '0'. In order to return back to normal mode, the

RESET_ARP bit has to be set to '1'

9.2

THS_P_L (0Ch)

User-defined threshold value for pressure interrupt event (Least significant bits) (R/W)

THS7

THS6

THS5

THS4

THS3

THS2

THS1

THS0

THS[7:0]

This register contains the low part of threshold value for pressure interrupt generation.

Default value: 00h

The threshold value for pressure interrupt generation is a 15-bit unsigned right-justified value composed of

THS_P_H (0Dh) and THS_P_L (0Ch).The value is expressed as:

THS_P (15-bit unsigned) = Desired interrupt threshold (hPa) x 16

To enable the interrupt event based on this user-defined threshold, the PHE bit or PLE bit (or both bits) in

INTERRUPT_CFG (0Bh) has to be enabled.

LPS22DF

THS_P_L (0Ch)

DS13316 - Rev 1

page 32/54

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