Using FIFO modes

AN4450

18/26

DocID025978 Rev 1

The whole FIFO content can be read by reading 3x32 bytes from PRESS_OUT_XL location

in a single I²C read transaction. Internally the reading address will automatically roll back

from 0x2A down to 0x28 when FIFO is active to allow a quick read of its content.

5.1.2

Bypass mode (F_MODE[2..0]="000" in FIFO_CTRL (0x2E))

The FIFO is not operational and for this reason the buffer remains empty. The pressure

value is sent directly to PRESS_OUT registers.

5.1.3

FIFO mode (F_MODE[2..0]="001" in FIFO_CTRL (0x2E))

The measurement from the sensor are sent to FIFO buffer, the FIFO content is read using

the registers PRESS_OUT_XL (0x28), PRESS_OUT_L (0x29) and PRESS_OUT_H (0x2A).

An interrupt can be enabled (WTM_EN bit[5] in CTRL_REG2 (0x21) in order to be raised

when the FIFO is filled to the level specified by the WTM_POINT[4..0] bits[4..0] in the

FIFO_CTRL (0x2E) register. The FIFO continues filling until it is full (32 slots of data for XL,

L and H). When full, the FIFO stops collecting incoming pressure measurements.

5.1.4

Stream mode (F_MODE[2..0]="010" in FIFO_CTRL (0x2E))

Like in FIFO mode the measurements are stored in the buffer before being available in

PRESS_OUT_XL, PRESS_OUT_L and PRESS_OUT_H. On the contrary of FIFO mode,

when full, the FIFO discards the older data as the new arrive. An interrupt can be enabled

and set as in FIFO mode though the same register FIFO_CTRL (0x2E).

Stream mode can be used to implement a digital filter averaging the samples stored in the

FIFO.

5.1.5

FIFO mean mode (F_MODE[2..0]="110" in FIFO_CTRL (0x2E))

This mode is used in order to enable the “low noise mode”. In this mode the pressure data

are stored in the FIFO after being averaged depending on AVGP[1..0] bit in register

RES_CONF (0x10).

Pressure data stored in the FIFO buffer are further averaged, to implement a moving

average, using a number of samples defined by WTM_POINT[3..0] in register FIFO_CTRL

(0x2E) and with the speed defined by ODR[2..0] in register CTRL_REG1 (0x20) the result is

placed in PRESS_OUT registers.

There are two possible ways to provide data output pressure averaged by FIFO:

1.

Same data rate (ODR setting) of data coming from sensor when the FIFO_MEAN_DEC

bit[4] of register CTRL_REG2 (0x21) is reset (0=Disable)

2.

Decimated output at 1 Hz when the FIFO_MEAN_DEC bit[4] of register CTRL_REG2

(0x21) is set (1=Enable)

In case 1, we will have the output data averaged by the last samples defined by

WTM_POINT[4..0] in register FIFO_CTRL (0x2E)