AN4650 datasheet(91/102 Pages) STMICROELECTRONICS

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AN4650

First-in first-out (FIFO) buffer

102

8.5.3

Example 3

Supposing the FIFO is storing data from the gyroscope, accelerometer and magnetometer

at different ODRs:

Gyroscope ODR = 104 Hz, Accelerometer ODR = 208 Hz, Magnetometer ODR = 52 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 FIFO_CTRL3 register has to be set to 010b (decimation

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

001b (no decimation applied to accelerometer data). Assuming that the magnetometer is

associated to the 3rd FIFO data set, the DEC_DS3_FIFO[2:0] field of theFIFO_CTRL4

The following data pattern is repeated every 21 samples:



Gx Gy Gz XLx XLy XLz Mx My Mz (gyroscope, accelerometer, magnetometer data - 9

samples)



XLx XLy XLz (accelerometer data - 3 samples)



Gx Gy Gz XLx XLy XLz (gyroscope and accelerometer data - 6 samples)



XLx XLy XLz (accelerometer data - 3 samples)

The FIFO_PATTERN_[9:0] bits will contain a number from 0 to 20, as shown in Table 73.

Table 73. Example 3: FIFO_PATTERN_[9:0] bits and next reading

Time

FIFO_PATTERN_[9:0]

Next reading from FIFO output registers

XLx

XLy

XLz

XLx

XLy

XLz

XLx

XLy

XLz

XLx

XLy

XLz

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