AN4506 datasheet(37/47 Pages) STMICROELECTRONICS

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AN4506

First-in first-out (FIFO) buffer

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The following steps are recommended for applications using FIFO mode:

Set FIFO_En = 1: enable FIFO;

Set FN[2:0] = (0,0,1): enable FIFO mode;

Wait for OVRN or FTH interrupt;

Read data from gyroscope output registers;

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

Repeat from step 2.

Figure 19. FIFO mode behavior

If FIFO mode is enabled, the buffer starts to collect data and fills all the 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 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. When the buffer is full, the FIFO index restarts from

the beginning and older data are replaced by current data. The oldest values continue to be

overwritten until a read operation makes FIFO slots available. The host processor reading

speed is important in order to free slots faster than the data rate. FM[2:0] bypass

configuration is used to stop this mode.

Follow these steps for Stream mode configuration:

Turn on FIFO by setting the FIFO_En bit to “1” in the CTRL5 register (0x24). After this

operation the FIFO buffer is enabled but is not collecting data, output registers are

frozen to the last sample set loaded.

Activate Stream mode by setting the FM[2:0] field to “010” in the FIFO_CTRL register

(0x2E).

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