AN4504 datasheet(34/41 Pages) STMICROELECTRONICS

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First-in first-out (FIFO) buffer

AN4504

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DocID026419 Rev 1

Figure 16. Stream mode slow reading behavior

In Figure 16, due to slow reading, data from “jj” are not retrieved because they are replaced

by the new gyroscope samples generated by the system.

Figure 17. Stream mode slow reading zoom

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

read procedure 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 shifted into the output registers in order to allow the next read operation. In the

case of a read slower than 1*ODR, some data can be retrieved from FIFO after that new

sample is inserted into the addressed location. In Figure 17 the fourth read command starts

after the refresh of the F3 index and this generates a disconnect in the data read. The

OVRN flag advises the user that this event has taken place. In this example, three correct

samples have been read, the number of correctly recovered samples is dependent on the

difference between the current ODR and the FIFO sample set read timeframe.

AN4504 Datasheet(PDF) 34 Page - STMicroelectronics