IIS2DLPC datasheet(34/69 Pages) STMICROELECTRONICS

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IIS2DLPC

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5.4

FIFO

The IIS2DLPC embeds 32 slots of 14-bit data FIFO for each of the three output channels, X,

Y and Z of the acceleration data. 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.

The internal FIFO allows collecting 32 samples (14-bit size data) for each axis.

When the FIFO mode is other than Bypass, reading the output registers (28h to 2Dh)

returns the oldest FIFO sample set. In order to minimize communication between the

master and slave, the address read may be automatically incremented by the device by

setting the IF_ADD_INC bit of CTRL2 (21h) to '1'; the device rolls back to 0x28 when

This buffer can work according to the following 5 different modes:



Bypass mode



FIFO mode



Continuous-to-FIFO



Bypass-to-Continuous



Continuous

Each mode is selected by the FMode[2:0] bits in the FIFO_CTRL (2Eh) register.

Programmable FIFO threshold is selected in FIFO_CTRL (2Eh). Status and FIFO overrun

events are available in the FIFO_SAMPLES (2Fh) register and can be used to generate

dedicated interrupts on the INT1 and INT2 pins using the CTRL4_INT1_PAD_CTRL (23h)

and CTRL5_INT2_PAD_CTRL (24h) registers.

FIFO_SAMPLES (2Fh) (FIFO_FTH) goes to '1' when the number of unread samples

FIFO_SAMPLES (2Fh) (Diff[5:0]) is greater than or equal to FTH[4:0] in FIFO_CTRL (2Eh).

If FTH[4:0] is equal to '0', FIFO_SAMPLES (2Fh) (FIFO_FTH) goes to '0'.

FIFO_SAMPLES (2Fh) (FIFO_OVR) is equal to '1' if a FIFO slot is overwritten.

FIFO_SAMPLES (2Fh) (Diff[5:0]) contains stored data levels of unread samples. When

Diff[5:0] is equal to ‘000000’, FIFO is empty. When Diff[5:0] is equal to ‘100000’, FIFO is full

and the unread samples are 32.

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

first sample acquired must be discarded.

When the FIFO threshold status flag is '0'-logic, FIFO filling is lower than the threshold level

and when '1'-logic, FIFO filling is equal to or higher than the threshold level.

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