Decimation Filter
28-48
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
Since the number range of the computed coefficients exceeds the range of the hardware, the coefficients
must be scaled, by at least a factor of 4. In this example, a factor of 8 is chosen.
below lists
the scaled values and their 24 bit signed fractional values, in hexadecimal notation.
28.5.2
Initialization Procedure
Specific initialization for two different operating modes is provided in the use case sections that follow this
section. The general sequence of steps for initializing one Decimation Filter is:
1. Program the configuration registers DECFILT_x_MCR to configure the input data source and
output result destination.
2. Write all filter coefficient registers DECFILT_x_COEFn with values that define the filter
frequency response characteristics.
3. Execute a soft reset if the filter was previously configured, by writing DECFILT_x_MCR[SRES]
= 1.
Table 28-19. Computed Coefficient Values
Coefficient
Decimal Value
Coefficient
Decimal Value
B0
0.0221455
A0
-1.0
B1
0.00445582948893748
A1
2.69772868375858
B2
0.0318517846509088
A2
-3.234056294853
B3
0.00445582948893748
A3
1.92028561712454
B4
0.0221455
A4
-0.47939080709495
Table 28-20. Coefficient Values for Decimation Filter
Computed Value
Scaled Value (SCAL=8)
Filter Coefficients
Decimal Value
Decimal Value
Hexadecimal Values
(24 bits)
DECFILT_x_COEF0 = B0/SCAL
0.0221455
0.00276815891266
0x005AB5
DECFILT_x_COEF1 = B1/SCAL
0.00445582948893748
0.00055694580078
0x001240
DECFILT_x_COEF2 = B2/SCAL
0.0318517846509088
0.00398147106171
0x008277
DECFILT_x_COEF3 = B3/SCAL
0.00445582948893748
0.00055694580078
0x001240
DECFILT_x_COEF4 = B4/SCAL
0.0221455
0.00276815891266
0x005AB5
DECFILT_x_COEF5 = A1/SCAL
2.69772868375858
0.33721613883972
0x2B29E6
DECFILT_x_COEF6 = A2/SCAL
–3.234056294853
–0.40425717830658
0xCC414E
DECFILT_x_COEF7 = A3/SCAL
1.92028561712454
0.24003565311432
0x1EB97D
DECFILT_x_COEF8 = A4/SCAL
–0.47939080709495
–0.05992400646210
0xF8546A
Summary of Contents for PXR4030
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Page 1167: ...Decimation Filter Freescale Semiconductor 28 53 PXR40 Microcontroller Reference Manual Rev 1...
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