LIS3DSH datasheet(21/53 Pages) STMICROELECTRONICS

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LIS3DSH

Digital main blocks

Doc ID 022405 Rev 1

21/53

5.2

FIFO

LIS3DSH embeds an acceleration data FIFO for each of the three output channels, X, Y,

and Z. This allows a 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 four

different modes: Bypass mode, FIFO mode, Stream mode and Stream-to-FIFO mode. Each

mode is selected by the FIFO_MODE bits. Programmable Watermark level, FIFO_empty or

FIFO_Full events can be enabled to generate dedicated interrupts on the INT1/2 pin.

5.2.1

Bypass mode

In Bypass mode, the FIFO is not operational and for this reason it remains empty. For each

channel only the first address is used. The remaining FIFO slots are empty.

5.2.2

FIFO mode

In FIFO mode, data from X, Y, and Z channels are stored in the FIFO. A Watermark interrupt

can be enabled in order to be raised when the FIFO is filled to the level specified by the

internal register. The FIFO continues filling until it is full. When full, the FIFO stops collecting

data from the input channels.

5.2.3

Stream mode

In Stream mode, data from the X, Y, and Z measurement are stored in the FIFO. A

Watermark interrupt can be enabled and set as in the FIFO mode. The FIFO continues filling

until it’s full. When full, the FIFO discards the older data as the new arrive.

5.2.4

Stream-to-FIFO mode

In Stream-to_FIFO mode, data from the X, Y, and Z measurement are stored in the FIFO. A

Watermark interrupt can be enabled in order to be raised when the FIFO is filled to the level

specified by the internal register. The FIFO continues filling until it’s full. When full, the FIFO

discards the older data as the new arrive. Once trigger event occurs, the FIFO starts

operating in FIFO mode.

5.2.5

Retrieve data from FIFO

FIFO data is read through the OUT_X, OUT_Y and OUT_Z registers. When the FIFO is in

Stream, Trigger or FIFO mode, a read operation to the OUT_X, OUT_Y or OUT_Z registers

provides the data stored in the FIFO. Each time data is read from the FIFO, the oldest X, Y,

and Z data are placed in the OUT_X, OUT_Y and OUT_Z registers and both single read and

read_burst operations can be used.

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