AN4506 Просмотр технического описания (PDF) - STMicroelectronics
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AN4506 Datasheet PDF : 47 Pages
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AN4506
First-in first-out (FIFO) buffer
Figure 21. Stream mode slow reading behavior
F0 F1 F2 F3 … … F31F0 . F? F?+1 . F31F0 F1 …
0 1 2 3 … … 31 32 . jj→xx kk→yy . 63 6465 …
FIFO Reading
F? F?+1 …
xx yy …
OVRN
Stream
enable
Start FIFO
Reading
Start FIFO
Reading
Samples
overwritten
t
AM08475v1
In Figure 21, due to slow reading, data from “jj” are not retrieved because they are replaced
by the new gyroscope samples generated by the system.
Figure 22. Stream mode slow reading zoom
F0 F1 F2 F3 F4 … F31 F0 F1 F2 F3 F4 …
…
0 1 2 3 4 … 31 32 33 34 35 36 …
…
t0
t
t0+dt
t0+31dt
FIFO Reading
R0:0 R1:1 R2:2 R3:35 R4:36
OVRN
Stream
enable
Start FIFO
Reading
Samples
overwritten
AM08476v1
After Stream mode has been enabled, FIFO slots are filled at the end of each ODR time
frame. The reading procedure must start as soon as the OVRN flag is set to “1”. Data are
retrieved from FIFO at the beginning of the reading operation. When a read command is
sent to the device, the output registers content 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. When reading is slower than 1*ODR, some data can be retrieved from FIFO after
that new sample is inserted into the addressed location. In Figure 22 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 samples correctly recovered depends on
the difference between the current ODR and the FIFO sample set reading time frame.
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