RFX144V24-S23 and RFX96V24-S23 Modem Designer’s Guide
1070
6-7
6.1.3 Filter
Coefficients
Table 6-1 contains the RAM access codes for all filter coefficients. Refer to the Section 4 for the proper procedure for writing
new coefficients into the RAM locations.
Table 6-2 contains the computed values of the filter coefficients, including those of default frequencies 462 Hz, 1100 Hz, and
2100 Hz. The value 32767 (7FFFh) is full scale in the DSP's machine units (i.e., 32767 = unity). Coefficients may range from
-1 to +1 (8000h to 7FFFh) in machine units. The sample rate is 9600 Hz.
6.2 TONE DETECTORS IN VOICE CODEC, AUDIO CODEC and AUDIO MODES
The tone detector coefficients must be reprogrammed when configured to Voice or Audio Codec modes that use either 4000
or 8000 Hz sample rates, and when configured for Audio mode using the 8000 Hz sample rate.
For a tone detector response time of 0.1 seconds (
τ
=0.1 sec.) and a sample rate of 4000 Hz (Fs=4000), set
α
" = 0051h and
β
” = 7FA8h.
Table 6-3 contains the computed values of the filter coefficients at the sample rate of 8000 Hz; and Table 6-4 contains the
computed values at a 4000 Hz sample rate.
Table 6-1. Filter Coefficient RAM Access Codes
RAM Write Access Code (Hex)
Coefficient Name
Tone 1
Tone 2
Tone 3
α
0
25
2B
31
α
1
26
2C
32
α
2
27
2D
33
α
'0
28
2E
34
α
'1
29
2F
35
α
'2
2A
30
36
β
1
A6
AC
B2
β
2
A7
AD
B3
β
'1
A9
AF
B5
β
'2
AA
B0
B6
α
”
A8
AE
B4
β
”
A5
AB
B1
Notes:
1. In all cases:
AREXx (x=1, 2) is a 0,
CRx (x= 1, 2) is a 1,
BRx (x= 1, 2) is a 0, and
DRx (x= 1,2) is a 0.
2. If the most significant bit (MSB) of the address is a 0, the data is written to
XRAM; if the MSB is a 1, the data is written to YRAM.
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