ASM330LXH datasheet(20/56 Pages) STMICROELECTRONICS

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ASM330LXH

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3.2

FIFO

The ASM330LXH 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

according to six different modes: Bypass mode, FIFO mode, Stream mode, Dynamic Stream

mode, Stream-to-FIFO mode and Bypass-to-Stream. Each mode is selected by the FMODE

[2:0] bits in the FIFO_CTRL (1Ah) register. Programmable FIFO threshold status, FIFO

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

(1Eh) register.

FIFO_SRC(FTH) goes to '1' when the number of unread samples (FIFO_SRC(FSS5:0)) is

greater than or equal to FTH [4:0] in FIFO_CTRL (1Ah). If FIFO_CTRL(FTH4:0) is equal to

0, FIFO_SRC(FTH) goes to ‘0’.

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

FIFO_SRC(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.

The FIFO feature is enabled by writing '1' in CTRL5_C (FIFO_EN).

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

3.2.1

Bypass mode

In Bypass mode (FIFO_CTRL(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.

Figure 8. Bypass mode

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