Cirrus Logic CDB6422 - Manual (Page 12)

CDB6422
12 DS295DB2
3.2.29 ext - EXT Jumper Set
A. Message indicating that the jumper EXT
is installed, allowing an external source to
configure the CS6422
B. No arguments needed
C. No pushes to the MSG Stack
3.2.30 d {number} - Dial Phone Number
A. Dials phone numbers up to 14 digits. A
‘,’ will add a small delay between numbers.
B. No pushes to the MSG Stack
C. Description:
3.2.31 ? - List Commands
A. Prints the list of available commands to
the UART
B. No arguments needed
C. No pushes to the MSG Stack
4. USAGE EXAMPLES
This section provides some examples of configura-
tion and use. All of the following examples assume
+12V operation (PWR_SEL1-4 = '+12V'), external
microphone plugged into 1/8" jack, and CS6422 in-
ternal mic preamp enabled.
4.1 CS6422 Usage Notes:
This section contains useful information regarding
the operation of the CS6422 in a system.
1) The CS6422 begins operation in half-duplex
mode. The device switches to full-duplex
mode automatically when both of its echo can-
cellers have trained.
2) If an echo canceller is enabled but no echo path
exists, then it will never train and the system
will remain in half-duplex. If an echo path does
not exist for the echo canceller, then the EC
should be disabled. For example, if there is no
coupling between NO and NI, the Network
Echo Canceller should be disabled by setting
NECD to ‘1’.
3) If the echo path is distorted (THD > 2%) then
the performance of the echo canceller will be
degraded, which can cause the device to remain
in half-duplex or to drop to half-duplex fre-
quently (during loud speech, for example).
Common sources of distortion are the speaker,
the speaker driver, and clipping at the A/D con-
verter at APO.
4) If the echo path is weak (gain between AO and
APO less than -30dB) then the echo canceller
will have difficulty adapting to the path and the
system will remain in half-duplex. A good goal
is to have a coupling gain between -20dB and -
6dB
5) The coupling gain must always be less than
0dB, otherwise a full-scale signal at AO or NO
will cause clipping at the associated A/D at
APO or NI, resulting in large amounts of distor-
tion which degrades echo canceller perfor-
mance.
6) The Acoustic Echo Canceller trains when there
is speech in the receive path (through RVol) but
not in the transmit path.
7) The Network Echo Canceller trains when there
is speech in the transmit path (through TVol)
but not in the receive path.
8) During full-duplex operation, if there is speech
in both transmit and receive paths (double-
talk), then neither echo canceller will train.
9) The echo cancellers will not train in the pres-
ence of any periodic signals (sine waves or mu-
sic, for example). Appropriate training signals
are voice and white noise.
4.2 Setting the Acoustic Coupling:
This section describes how to adjust the mic
preamp gain or the speaker/mic position to set the