AN3393 datasheet(95/103 Pages) STMICROELECTRONICS

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AN3393

First-in first-out (FIFO) buffer

103

FIFO sample set (6 bytes) is read faster than 1*ODR: data are correctly retrieved

because a free slot is made available before new data is generated.

FIFO sample set (6 bytes) is read synchronous to 1*ODR: data are correctly retrieved

because a free slot is made available before new data is generated but FIFO benefits

are not exploited. This case is equivalent to reading data on the data-ready interrupt

and does not reduce interaction by the host processor compared to the standard

accelerometer reading.

FIFO sample set (6 bytes) is read slower than 1*ODR: in this case some data is lost

because data recovery is not fast enough to free slots for new acceleration data,

Figure 31. The number of correctly recovered samples is related to the difference

between the current ODR and the reading rate of the FIFO sample set.

Figure 31. Stream mode slow reading behavior

In Figure 31, due to slow reading, data from “jj” are not retrieved because they are replaced

by the new acceleration samples generated by the system.

Figure 32. Stream mode slow reading zoom

After Stream mode enable, FIFO slots are filled at the end of each ODR time frame. The

read must start as soon as the OVRN flag is set to “1”, data are retrieved from FIFO at the

beginning of the read operation. When a read command is sent to the device, the content of

the output registers is moved to the SPI/I2C register and the current oldest FIFO value is

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