AN4504 datasheet(32/41 Pages) STMICROELECTRONICS

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First-in first-out (FIFO) buffer

AN4504

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DocID026419 Rev 1

A FIFO mode application hint is given below:

Set FIFO_EN = 1: Enable FIFO

Set FM[2:0] = (0,0,1): Enable FIFO mode

Wait for the OVRN or WTM interrupt

Read data from the gyroscope output registers

Set FM[2:0] = (0,0,0): Enable Bypass mode

Repeat from step 2

Figure 14. FIFO mode behavior

If FIFO mode is enabled, the buffer starts to collect data and fills all 32 slots (from F0 to F31)

at the selected output data rate. When the buffer is full, the OVRN bit goes high and data

collection is permanently stopped; the user can decide to read FIFO content at any time

because it is maintained unchanged until Bypass mode is selected. The read procedure is

composed of a 32 sample set of 6 bytes for a total of 192 bytes and retrieves data starting

from the oldest sample stored in FIFO (F0). The OVRN bit is reset when the first sample set

has been read. The Bypass mode setting resets FIFO and allows the user to enable FIFO

mode again.

6.3.3

Stream mode

In Stream mode FIFO continues filling and when the buffer is full, the FIFO index restarts

from the beginning and older data is replaced by the current. The oldest values continue to

be overwritten until a read operation frees FIFO slots. The host processor reading speed is

most important in order to free slots faster than new data is made available. FM[2:0] bypass

configuration is used to stop this mode.

Follow these steps for FIFO mode configuration:

Turn on FIFO by setting the FIFO_EN bit to “1” in control register 5 (0x24). After this

operation the FIFO buffer is enabled but isn’t collecting data, output registers are

frozen to the last samples set loaded.

Activate Stream mode by setting the FM[2:0] field to “011” in the FIFO control register

(0x2E).

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