Decimation Filter
Freescale Semiconductor
28-31
PXR40 Microcontroller Reference Manual, Rev. 1
Figure 28-16. Convergent Rounding Methodology
28.3.11 Saturation
Filter output saturation occurs when an overflow or underflow condition of the filter is detected by
dedicated logic, and if it is enabled by the SAT control bit of the configuration register DECFILT_x_MCR.
In this condition, the filter output is set to a saturated value equal to the maximum or minimum value that
can be represented by the 16-bit output port. Also, for the IIR filter an equivalent logic is used to assert the
saturation for the 24-bit feedback result.
28.3.12 Interrupts and DMA Overview
There are several host request events that can be enabled using the module configuration register (MCR).
An interrupt request can be issued under any of the following conditions:
•
when a word of input data is received
•
when the input buffer can receive data
•
when a word of output data is available
•
when an error has occurred.
The input data flag DECFILT_x_MSR[IDF] is set when a new input data is received from the CPU or an
eQADC. Note that this flag is not used to generate read or write requests (as defined in
Input Buffer Interrupt and DMA Requests
Output data is available and its flag (DECFILT_x_MSR[ODF]) is set when the input data sample is
processed by the filter, the decimation counter matches the decimation rate value, and it is moved to the
output buffer. It is not used to generate read requests (as defined in
Section 28.3.12.2, Output Buffer
).
An error event in the decimation filter block is defined as one of these events:
•
Overflow in the filter, flagged by DECFILT_x_MSR[OVF]
•
Overrun in the decimation filter input, flagged by DECFILT_x_MSR[IVR]
•
Overrun in the decimation filter output, flagged by DECFILT_x_MSR[OVR]
xx.......xx.......0010
1
xx.......xx.......00100
xx...xx
1000.....00......00
Before Rounding
xx.......xx.......00100
xx...xx
Rounded Down
MS_WORD
LS_WORD
+0
xx...xx
1000.....00......00
Before Rounding
xx.......xx.......00110
xx...xx
Rounded Up
+1
Summary of Contents for PXR4030
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