User`s manual

AMBE-2000™ Vocoder Chip
User’s Manual Version 4.9
DVSI Confidential Proprietary, Subject to Change Page 41
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7 Special Functions
7.1 Hardware vs. Software Selection Note
Many of the functions of the AMBE-2000™ can be accessed through both 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, ECHOCAN_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-2000™. These rates are
selected by using the 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 pre-configured 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