User`s manual

AMBE-2000™ Vocoder Chip
User’s Manual Version 4.9
DVSI Confidential Proprietary, Subject to Change Page 28
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5.2.1 Framed Input: Word 0 : Header
The decoder uses the header information to synchronize with the beginning of each 20 millisecond frame. This 16-bit word
MUST be 0x13EC.
5.2.2 Framed Input: Word 1 : Power Control ID
Set the 8-bit Power Control ID field to 0x00 for normal use. For Power Down Mode, set this value to 0x55. This causes the
AMBE-2000™ to enter low power mode. To exit low power mode, the device must be reset through the hardware.
Table 5-A Framed Input: Power Control ID Values Summary
ID Type Description
0x00 Voice Data This ID value instructs AMBE-2000™ to operate in normal fashion
0x55 Low Power Mode
When this mode is activated the AMBE-2000™ Vocoder Chip will go into a mode,
which conserves power, where no voice packets are being processed.
5.2.3 Framed Input: Word 1 : Control Word 1
Use the 8-bit control word to set various functions.
Table 5-B Control Word 1 Format
Control Word 1 – 8-bits (See Table 1-F)
7: MSB 6 5 4 3 2 1 0 : LSB
Lost Frame
Indicator
Unused Unused Unused Unused Unused
CNI
Unused
Lost Frame Indicator: Setting the Lost Frame Indicator bit to a 1 will cause the AMBE-2000™ decoder to construct the
voice frame using the parameters from the previous frame. This is an effective way to mask the effects of short periods of data
loss. The user should set this bit when channel data is lost or corrupted. It works by replacing the frame of corrupted data with
the previous, intact, frame.
Comfort Noise Insertion (CNI): Setting the CNI bit will cause the decoder to output a frame of comfort noise. This bit is
used with systems that are capable of discontinuous transmission (DTX).
5.2.4 Framed Input: Words 2-6 : Rate Information
Rate Info 0, Rate Info 1, Rate Info 2, Rate Info 3, Rate Info 4
The initial rate of the AMBE-2000™ is set through the hardware pins RATE_SEL [4-0] (see Section 7.2 and Tables 7-A and 7-
B). After resetting the device, the coding rate can be modified for both the encoder and the decoder by sending a framed
packet to the input channel interface. The Rate Selector control field (described in section 5.2.9) determines where to apply the
rate change.
The AMBE-2000™ uses these five words to set the source and FEC coding rates. Tables 5-C and 5-D list predefined values for
various source and FEC rates. These are only a representation of the most common rates that are requested. Please contact
DVSI for additional rate information if the desired rates are not listed. The software configurations in Table 5-C are
compatible for use with the AMBE-1000™ (using AMBE™ technology). If compatibility is not an issue, use the software
codes in Table 5-D to select speech and FEC rates to optimize use of the AMBE-2000™ (using AMBE+™ technology).