MPC563XM Reference Manual, Rev. 1
1142
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
Equation 4
The coefficient results in fixed point decimal representation is shown in
Comparing Equation 3 with Equation 4, we obtain the relationship between the calculated values of
coefficients and the values to be loaded in the DECFILTER_COEFn registers. Refer to
to obtain the coefficients. Note that we are using the scale factor 8 because is the smallest divider factor to
have all coefficient values in the range (-1 <= Coef < +1).
25.8.2
Input Data Calculation
The input data are samples of a sum of two tones: one tone of 30 kHz and another tone of 250 kHz. The
samples was calculated at the rate of 800k samples per second. The tones have the same amplitude and it
is assured the resultant amplitude is smaller than 1 to obtain samples in the range (-1 <= sample < +1). It
is supposed the input data are signed values in the 2-complement format in the range (-1 <= sample < +1).
Table 25-8. Coefficient values given by SPW digital filter design tool
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 25-9. Coefficient values for Decimation Filter
SCALE
S=1
S=8
COEFn
Decimal Value
Decimal Value
Hexa. Values
(24 bits)
Coef0 = B0/S
0.0221455
0.00276815891266
0x005AB5
Coef1 = B1/S
0.00445582948893748
0.00055694580078
0x001240
Coef2 = B2/S
0.0318517846509088
0.00398147106171
0x008277
Coef3 = B3/S
0.00445582948893748
0.00055694580078
0x001240
Coef4 = B4/S
0.0221455
0.00276815891266
0x005AB5
Coef5 = -A1/S
2.69772868375858
0.33721613883972
0x2B29E6
Coef6 = -A2/S
-3.234056294853
-0.40425717830658
0xCC414E
Coef7 = -A3/S
1.92028561712454
0.24003565311432
0x1EB97D
Coef8 = -A4/S
-0.47939080709495
-0.05992400646210
0xF8546A
y n
( )
B
0
x n
( )
B
1
x n
1
–
(
)
B
2
x n
2
–
(
)
B
3
x n
3
–
(
)
B
4
x n
4
–
(
)
+
+
+
+
A
0
A
1
y n
1
–
(
)
–
A
2
y n
2
–
(
)
–
A
3
y n
3
–
(
)
–
A
4
y n
4
–
(
)
–
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=
Содержание MPC5632M
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