AN4650 datasheet(92/102 Pages) STMICROELECTRONICS

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First-in first-out (FIFO) buffer

AN4650

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DocID027415 Rev 1

8.6

FIFO threshold

The FIFO threshold is a functionality of the LSM6DS3 FIFO which can be used to check

when the number of samples in the FIFO reaches a defined threshold level.

The bits FTH_[11:0] in the FIFO_CTRL1 and FIFO_CTRL2 registers contain the threshold

level. The resolution of the FTH_[11:0] field is two bytes (1 LSB = 2 Bytes, each sample is

represented as 16-bit data). So, the user can select the desired level in a range between 0

and 4095.

The bit FTH in the FIFO_STATUS2 register represents the watermark status. This bit is set

high if after the next FIFO write operation the number of samples in the FIFO reaches or

exceeds the watermark level (each sample is represented as 16-bit data). When the FIFO is

configured in Continuous mode or in Bypass-to-Continuous mode, the FTH bit can be used

to catch when the number of samples in the FIFO reaches the threshold level. In the other

FIFO modes, the FIFO_FULL bit in the FIFO_STATUS2 register has to be used for this

purpose.

FIFO size can be limited to the threshold level by setting the STOP_ON_FTH bit in the

CTRL4_C register to 1.

Figure 29. FIFO threshold (STOP_ON_FTH = 0)

Figure 29 shows an example of FIFO threshold level usage when just accelerometer (or

gyroscope) data are stored. The STOP_ON_FTH bit set to 0 in the CTRL4_C register. The

threshold level is set to 21 through the FTH[11:0] bits. The FTH bit of the FIFO_STATUS2

STOP_ON_FTH bit is set to 0, the FIFO will not stop at the 21st sample, but will keep storing

data until the FIFO_FULL flag is set high.

AN4650 Datasheet(PDF) 92 Page - STMicroelectronics