LSM330 datasheet(22/75 Pages) STMICROELECTRONICS

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Functionality

LSM330

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DocID023426 Rev 3

4.2.3

Bypass mode

In Bypass mode, the FIFO is not operational and it remains empty. For each channel only

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

Bypass mode must be used in order to reset the FIFO buffer when a different mode is

operating (i.e. FIFO mode).

4.2.4

FIFO mode

In FIFO mode, the buffer continues filling data from the X, Y and Z accelerometer channels

until it is full (set of 32 samples stored). When the FIFO is full it stops collecting data from

the input channels and the FIFO content remains unchanged.

An overrun interrupt can be enabled, P1_OVERRUN = '1' in the CTRL_REG7_A (25h)

occurs, the first data has been overwritten and the FIFO stops collecting data from the input

channels.

At the end of the reads it is necessary to transition from Bypass mode to reset FIFO content.

After this reset command it is possible to restart FIFO mode by writing '001' to FMODE [2:0]

in the FIFO_CTRL_REG_A (2Eh) register.

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

be reduced by a programmable watermark. In order to enable a FIFO watermark, the

WTM_EN bit in CTRL_REG7_A (25h) is high and the FIFO depth is set by the WTMP [4:0]

bits in the FIFO_CTRL_REG_A (2Eh) register. The watermark interrupt can be enabled on

the INT1_A pad if the P1_WTM bit in the CTRL_REG7_A (25h) register is enabled.

4.2.5

Stream mode

In Stream mode FIFO continues filling data from the X, Y, and Z accelerometer channels.

When the buffer is full (set of 32 samples stored) the FIFO buffer index restarts from the

beginning and older data is replaced by the current. The oldest values continue to be

overwritten until a read operation makes free FIFO slots available.

An overrun interrupt can be enabled, P1_OVERRUN = '1' in the CTRL_REG7_A (25h)

not to lose data 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 WTMP [4:0] bit in the FIFO_CTRL_REG_A (2Eh) register 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 already read in the previous burst, so the number of new data

available in FIFO depends on the previous reading (see FIFO_SRC_REG_A (2Fh)).

At the end of the reads it is necessary to transition from Bypass mode to reset FIFO content.

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