LIS2HH12 datasheet(20/47 Pages) STMICROELECTRONICS

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Digital main blocks

LIS2HH12

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DocID025344 Rev 5

5.3.2

FIFO mode

In FIFO mode (FIFO_CTRL (2Eh) (FMODE [2:0])= 001) data from the X, Y and Z channels

are stored in the FIFO until it is full. An overrun interrupt can be enabled, CTRL3 (22h)

(INT1_OVR)= '1', in order to be raised when the FIFO stops collecting data. When the

overrun interrupt occurs, the first set of data has been overwritten and the FIFO stops

collecting data from the input channels. To reset the FIFO content, Bypass mode should be

written in the FIFO_CTRL (2Eh) register, setting the FMODE [2:0] bits to '000'. After this

reset command, it is possible to restart FIFO mode, writing the value '001' in FIFO_CTRL

(2Eh) (FMODE [2:0]).

The FIFO buffer can memorize 32 slots of X, Y and Z data, but the depth of the FIFO can be

reduced using the CTRL3 (22h) (STOP_ FTH) bit. Setting the STOP_FTH bit to '1', FIFO

depth is limited to FIFO_CTRL (2Eh) (FTH [4:0]) - 1.

5.3.3

Stream mode

Stream mode (FIFO_CTRL (2Eh) (FMODE [2:0]) = 010) provides a continuous FIFO

update: as new data arrives, the older data is discarded.

An overrun interrupt can be enabled, CTRL3 (22h) (INT1_OVR) = '1', in order to read the

entire content of the FIFO at once. If in the application no data can be lost and it is not

possible to read at least one sample for each axis within one ODR period, a watermark

interrupt can be enabled in order to read partially the FIFO and leave free memory slots for

incoming data. Setting the FIFO_CTRL (2Eh) (FTH [4:0]) to value N, the number of X, Y and

Z data samples that should be read at the rise of the watermark interrupt is up to (N+1).

In the latter case, reading all FIFO content before an overrun interrupt has occurred, the first

data read is equal to the last data already read in previous burst, so the number of new data

available in the FIFO depends on the previous reading (see FIFO_SRC (2Fh)behavior

depicted in the following figures).

Figure 6. Stream mode

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