AN4650 datasheet(90/102 Pages) STMICROELECTRONICS

90 / 102 page

First-in first-out (FIFO) buffer

AN4650

90/102

DocID027415 Rev 1

8.5.2

Example 2

Supposing the FIFO is storing data from the gyroscope and accelerometer at different

ODRs:



Gyroscope ODR = 208 Hz, Accelerometer ODR = 104 Hz.

If the internal trigger (accelerometer/gyroscope data-ready) is used, it’s recommended to set

the ODR_FIFO_[3:0] bits of the FIFO_CTRL5 register to 0101b in order to set the FIFO

trigger ODR to 208 Hz.

The DEC_FIFO_GYRO[2:0] field of theFIFO_CTRL3 register has to be set to 001b (no

decimation applied to gyroscope data) and the DEC_FIFO_XL[2:0] field has to be set to

010b (decimation with factor 2 applied to accelerometer data).

Since the gyroscope ODR is twice the accelerometer ODR, the following data pattern is

repeated every 9 samples (each sample is represented as 16-bit data):



Gx Gy Gz XLx XLy XLz Gx Gy Gz

The FIFO_PATTERN_[9:0] bits will contain a number from 0 to 8, as shown in Table 72.

Table 71. Example 1: FIFO_PATTERN_[9:0] bits and next reading

Time

FIFO_PATTERN_[9:0]

Next reading from FIFO output registers

XLx

XLy

XLz

Table 72. Example 2: FIFO_PATTERN_[9:0] bits and next reading

Time

FIFO_PATTERN_[9:0]

Next reading from FIFO

output registers

XLx

XLy

XLz

AN4650 Datasheet(PDF) 90 Page - STMicroelectronics