AMBE-2000™ Vocoder Chip

User’s Manual Version 3.0

page 38

Confidential Proprietary, Subject to Change

7 Special Functions

7.1

Hardware vs. Software Selection Note

Many of the functions of the AMBE-2000™ 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, 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 Control Word interface described in section 5.3.4. 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 a Control Word as described in section 5.3.4, 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 16 preconfigured voice/FEC rates. The voice and FEC

rates are individually configurable in 50 bit per second intervals. If rates other than these are desired then the Control Word

method of configuring the rates must be used.

Table 7-A Rate Selection Using Rate Info 0-4, compatible w/ AMBE-1000™

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