LPS225HB datasheet(14/47 Pages) STMICROELECTRONICS

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FIFO

LPS225HB

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DocID030115 Rev 2

FIFO

The LPS225HB embeds 32 slots of 40-bit data FIFO to store the pressure and temperature

output values. This allows consistent power saving for the system, since the host processor

does not need to continuously poll data from the sensor, but it can wake up only when

needed and burst the significant data out from the FIFO. This buffer can work according to

seven different modes: Bypass mode, FIFO mode, Stream mode, Dynamic-Stream mode,

Stream-to-FIFO mode, Bypass-to-Stream and Bypass-to-FIFO mode. The FIFO buffer is

enabled when the FIFO_EN bit in CTRL_REG2 (11h) is set to '1' and each mode is selected

by the FIFO_MODE[2:0] bits in FIFO_CTRL (14h). Programmable FIFO threshold status,

FIFO overrun events and the number of unread samples stored are available in the

FIFO_STATUS (26h) register and can be set to generate dedicated interrupts on the

INT_DRDY pad using the CTRL_REG3 (12h) register.

FIFO_STATUS (26h)(FTH_FIFO) goes to '1' when the number of unread samples

(FIFO_STATUS (26h)(FSS5:0)) is greater than or equal to WTM[4:0] in FIFO_CTRL (14h).

If FIFO_CTRL (14h)(WTM4:0) is equal to 0, FIFO_STATUS (26h)(FTH_FIFO) goes to '0'.

FIFO_STATUS (26h)(OVRN) is equal to '1' if a FIFO slot is overwritten.

FIFO_STATUS (26h)(FSS5:0) contains stored data levels of unread samples; when

FSS[5:0] is equal to '000000', FIFO is empty, when FSS[5:0] is equal to '100000', FIFO is full

and the unread samples are 32.

To guarantee the switching into and out of FIFO mode, discard the first sample acquired.

4.1

Bypass mode

In Bypass mode (FIFO_CTRL (14h)(FMODE2:0)=000), the FIFO is not operational and it

remains empty.

Bypass mode is also used to reset the FIFO when in FIFO mode.

As described in the next figure, for each channel only the first address is used. When new

data is available, the older data is overwritten.

Every time Bypass mode is selected, FIFO content is flushed.

Figure 5. Bypass mode

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