RM0029 Datasheet, PDF (1194/1740 Pages) STMicroelectronics – The primary objective of this document

Decimation Filter
RM0029
Normal mode
This is the default operational mode of the decimation filter block. It corresponds to the
prefill/filter operation with input data supplied through the PSI slave-bus interface (i.e. its
input data is the ADC conversion result), with output going to the same PSI interface.
Standalone mode
Standalone mode differs from normal mode because the input data is not supplied by the
master block through the PSI slave-bus interface. In this case, the data is provided by the
central processor using the device slave-bus interface or DMA interface signals. Once the
data is filtered the decimated result is available in the Output Buffer register. The filter output
is also consumed by a CPU or DMA mastering the same device slave-bus interface. This
operation mode can be used to debug the filter stability or to decimate data in System RAM.
PSI Input Mixed mode
In this mode the input is selected from the PSI slave-bus interface, but the output is directed
to the device slave-bus interface, where it can be read by the CPU or DMA.
PSI Output Mixed mode
This mode works inverted from the PSI Input Mixed Mode: the input is selected from the
device slave-bus interface, fed either by the CPU or DMA, and the output is directed to the
PSI slave-bus interface. If an eQADC is connected to the PSI interface, the output is
directed to an RFIFO selected by the tag field in the DECFILTER_IB register (see Section ,
Decimation Filter Interface Input Buffer Register (DECFILTER_IB)).
Cascade mode
Cascade mode is a filter structure mode with two or more individual filter blocks connected
in a chain to form a more complex filter function. The output result of the first block (head
block) is connected to the input of the next block (middle or tail block) to be filtered again.
More details in Section 26.5.16, Cascade mode description.
Low Power mode
Low power mode corresponds to the module disable mode or stop mode. In the module
disable mode the PSI slave-bus line is disabled and it is not possible to enter Freeze mode.
The system clock is stopped. And in stop mode, the system clock is also stopped.
Freeze mode
This mode is also known as debug mode. All filter action is frozen, either through software
or by the hardware SoC debug request signal. If a freeze request comes when the filter is
processing an input, it enters freeze mode only after the processing finishes.
26.3
Note:
26.3.1
External signal description
The Decimation Filter does not provide metastability protection nor filtering for these signals.
Decimation trigger signal
This signal is used to control the output of the decimation filter, allowing decimation to be
driven externally. For more details, see Section , Triggered output result description.
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