LPS25H datasheet(38/45 Pages) STMICROELECTRONICS

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FIFO operating details

LPS25H

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DocID023722 Rev 5

FIFO operating details

8.1

FIFO registers

This device embeds a 32-slot x 24 bit FIFO pressure data coming from the PRESS_OUT

(@ 28..2Ah). It allows lower frequency of serial bus transactions and provides more time to

collect all taken measurements. The FIFO can operate in the following modes:

The mode is defined by 3 bits @0x2E: FIFO_CTRL. F_MODE[2:0]

BYPASS MODE [000]

In this mode the FIFO is disabled and stays empty. Pressure is ready directly.

FIFO MODE [001]

All pressure measurement are filling the FIFO. The FIFO content is read by reading the

PRESS_OUT registers @28..2Ah). A watermark interrupt can be enabled (CTRL2.

WTM_EN) which is raised when the FIFO is filled to the level specified in FIFO_CTRL.

WTM_POINT[4:0]. When the FIFO is full, the FIFO stops collecting incoming pressure

measurements.

BYPASS TO STREAM MODE [100]

The FIFO is in BYPASS mode till the trigger event. Then the STREAM MODE starts

FIFO MEAN Mode [110] & FIFO_mean_dec = 0

In this mode, the FIFO is used in STREAM mode and its content can be averaged by HW.

The hardware calculated running (moving) average can be read in PRESS_OUT registers

at anytime. This is used to further reduce the pressure noise at low power.

The number of samples to average is selectable through WTM_POINT[4:0]. See Table 22.

BYPASS to FIFO mode [111]

The FIFO switch from BYPASS to FIFO mode when the event is asserted

Accessing the FIFO data:

FIFO data is read through PRESS_OUT registers. When FIFO is in Stream, Trigger or FIFO

mode, a read operation to the PRESS_OUT registers provide the data stored in the FIFO.

Each time data is read from the FIFO, the oldest entry is placed in the PRESS_OUT

registers and both single read and burst read operation can be used.

Table 22. Running average sample size

WTM_POINT[4:0]

Sample averaged

00001

00011

00111

01111

11111

others

Reserved

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