LSM9DS1 datasheet(23/72 Pages) STMICROELECTRONICS

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LSM9DS1

LSM9DS1 functionality

3.5

Accelerometer and gyroscope FIFO

The LSM9DS1 embeds 32 slots of 16-bit data FIFO for each of the gyroscope’s three output

channels, yaw, pitch and roll, and 16-bit data FIFO for each of the accelerometer’s three

output channels, X, Y and Z. 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

accordingly to five different modes: Bypass mode, FIFO-mode, Continuous mode,

Continuous-to-FIFO mode and Bypass-to-Continuous. Each mode is selected by the

FMODE [2:0] bits in the FIFO_CTRL (2Eh) register. Programmable FIFO threshold status,

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

FIFO_SRC (2Fh) register and can be set to generate dedicated interrupts on the INT1_A/G

pin in the INT1_CTRL (0Ch) register and on the INT2_A/G pin in the INT2_CTRL (0Dh)

FIFO_SRC (2Fh)(FTH) goes to '1' when the number of unread samples (FIFO_SRC (2Fh)

(FSS5:0)) is greater than or equal to FTH [4:0] in FIFO_CTRL (2Eh). If FIFO_CTRL (2Eh)

(FTH[4:0]) is equal to 0, FIFO_SRC (2Fh)(FTH) goes to ‘0’.

FIFO_SRC (2Fh)(OVRN) is equal to '1' if a FIFO slot is overwritten.

FIFO_SRC (2Fh)(FSS [5:0]) 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.

The FIFO feature is enabled by writing '1' in CTRL_REG9 (23h) (FIFO_EN).

To guarantee the correct acquisition of data during the switching into and out of FIFO mode,

the first sample acquired must be discarded.

3.5.1

Bypass mode

In Bypass mode (FIFO_CTRL (2Eh)(FMODE [2:0]= 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 Figure 10, for each channel only the first address is used. When new data is

available the old data is overwritten.

Figure 10. Bypass mode

x31

y31

z31

xi,yi,zi

empty

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