Programming Information
63
1.
Determine the filter range by evaluating the following:
Filter Range (f
h
) = Demod f
c
- (2 x Symbol Rate)
Filter Range (f
h
) = 8000 - (2 x 1000) = 6000Hz
2.
Using the results of Step 1, select the coefficients K
0
, K
1
, K
2
, and K
3
from
Table
3.5.28
:
K
0
= -1.01 x 10
-12
K
1
= 7.17 x 10
-8
K
2
= 3.9 x 10
-3
K
3
= -16
3.
Using the coefficients selected in Step 2, evaluate the following equation:
HP Filter = (K
0
x f
h
3
) + (K
1
x f
h
2
) + (K
2
x f
h
) + K
3
HP Filter = (-.22) + (2.58) + (23.4) -16 = 9.76
4.
Rounding the value from step results in HP Filter = 10. This value is within the
range of 0-255 so no limiting is required.
5.
Converting the number to a hexadecimal value results in a 0Ah which is
written to register 39h.
3.5.22 Register 3Ah (75h), Modulator Low Pass Filter Tuning
This register selects the modulator low pass filter setting.
Figure 3.5.22
illus-
trates the breakout of register bit assignments.
Figure 3.5.22: Register 3Ah Bit Assignments
Table 3.5.29: Modulator Low Pass Filter Tuning Register Definition
7
6
5
4
3
2
1
0
0/1
0/1 0/1
0/1
0/1
0/1
0/1
0/1
Mod LP Filter Select [Bit weight = 1] LSB
Mod LP Filter Select [Bit weight = 2]
Mod LP Filter Select [Bit weight = 4]
Mod LP Filter Select [Bit weight = 8]
Mod LP Filter Select [Bit weight = 16]
Mod LP Filter Select [Bit weight = 32]
Mod LP Filter Select [Bit weight = 64]
Mod LP Filter Select [Bit weight = 128] MSB
Bit No.
Bit Name(s)
Functional Description
07-00
Mod Low Pass Filter Tuning
(See steps below)
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