AMBE-2000™ Vocoder Chip Users Manual
Version 4.92, June, 08
DVSI Confidential Proprietary, Subject to Change
Page 43
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7
Special Functions
7.1
Hardware vs. Software Selection Note
Many of the functions of the AMBE-2020™ can be accessed through both a hardware and software interfaces to the device.
The following hardware inputs, CHANN_SEL[1-0], RATE_SEL[4-0], CODEC_SEL[1-0], VAD_EN, ENCODER_EN, and
SLEEP_EN, are only accessed for input during the first 200 microseconds after a hardware reset on RESETN. For
predictable operation these signals must remain stable over this time period. After this initialization period the functions
that these pins access can only be reconfigured through the channel interface described in section 5.2. Changes on these
pins after the 200 microseconds initialization period after reset are ignored, unless another reset is performed.
7.2
Coding Rate Selection
The Voice coding rate as well as the FEC coding rate can be selected individually on the AMBE-2020™. These rates are
selected by using Rate Info words as described in section 5.2.4, or through hardware pins RATE_SEL[4-0] subject to the
restrictions in section 7.1. The five input pins RATE_SEL[4-0] give 32 preconfigured voice/FEC rates. If rates other than
these are desired then the Rate Info Words (in the Framed channel interface) can be used to configure voice and FEC rates
in 50 bps increments.
Table 7-A Rate Selection Using Rate Info 0-4, compatible w/ AMBE-1000™ (AMBE™)
RATE_SEL4
Pin
RATE_SEL3
Pin
RATE_SEL2
Pin
RATE_SEL1
Pin
RATE_SEL0
Pin
Speech Rate
(bps)
FEC Rate (bps)
Total Rate
(bps)
0
0
0
0
0
2400
0
0
0
1
0
1
2350
50
2400
0
0
0
0
1
3600
0
0
1
0
1
1
3350
250
3600
0
1
1
1
1
4000
0
0
1
1
1
0
3750
250
4000
0
0
0
1
1
4800
0
0
0
1
1
1
4550
250
0
0
0
1
0
3600
1200
0
1
0
0
0
3100
1700
4800
0
1
0
1
0
4150
2250
6400
0
1
0
0
1
4400
2800
7200
0
1
1
0
0
7750
250
0
1
1
0
1
4650
3350
8000
0
0
1
0
0
9600
0
0
0
1
1
0
4850
4750
9600
