5 Channel Data Format

The channel interface is responsible for outputting the compressed data from the encoder and inputting compressed data to the

decoder. In addition to these most basic functions the channel interface is also capable of reporting certain events, such as the

detection of a DTMF tone. The channel interface can also control certain selectable functions of the AMBE-2000™, such as

the voice coding rate. This chapter will describe how the AMBE-2000™ uses the channel interface to multiplex these

capabilities.

There are two formats to the data, Formatted and Unformatted, both of which operate in serial mode. Generally speaking the

Unformatted mode is used only when the connection between the AMBE-2000™ and the channel under design is relatively

direct, and the designer wants to simplify the extraction of the relevant voice data. In this mode configuration is accomplished

using hardwired pins. In most cases, when a controller is present between the AMBE-2000™ and the channel, the system

designer will find that using the Formatted format is more flexible.

5.1

Formatted Format

The Formatted format is a 24 by sixteen-bit word format for a total of 48 bytes or 384 bits. Every 20 milliseconds the encoder

outputs 24 sixteen-bit words, and likewise the decoder expects to receive 24 words. The format of the input and output frames

are detailed below. The first 12 sixteen bit words are made up of header, ID and status or control information. The remaining

12 sixteen bit words make up the encoded data bit field. These 12 words, or 192 bits, will be fully populated with relevant

voice data only when the AMBE-2000 is operating in a 9600bps mode (9600 bits/sec

Otherwise, when the data rate is less than 9600bps, the coded voice bits are filled starting from the MSB of the first word in the

field, leaving any unused bits as zeros. It is important to note here that even when the AMBE-2000 is operating at less than

9600bps, all 384 bits of the Formatted format (including any unused trailing zeros) must be transferred out of the encoder and

into the decoder.

5.2

Formatted Input Format

The format of the Formatted input is shown in Figure 5-A. Keep in mind that even though the channel data in this Formatted

input format is closely associated with the decoder, the control information will apply to both encoder and decoder functions.