CDB6420 Cirrus Logic Inc, CDB6420 Datasheet - Page 19

• Manufacturer Part Number: CDB6420
• Description: Development Kit
• Manufacturer: Cirrus Logic Inc

Specifications of CDB6420

• Silicon Manufacturer: Cirrus Logic
• Application Sub Type: Speakerphone
• Kit Application Type: Audio / Video / TV
• Silicon Core Number: CS6420
• Kit Contents: Board
• Kit Features: Analog And Digital Patch Area
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Threshold
The sensitivity of the speech detector controls
channel switching and ownership in half-duplex
mode. The transmit speech detector registers
speech if the transmit channel signal power is TH-
Det above the noise floor of the transmit channel.
TSAtt - Transmit Suppression Attenuation
This parameter sets the amount of suppression at-
tenuation inserted into the transmit path when
transmit suppression is engaged.
TSBias - Transmit Suppression Bias
The bias level affects the ease with which near-end
speech may break-in or be crushed by far-end
speech. See the Design Considerations section on
Transmit Suppression for full details.
TSThd - Transmit Suppression Threshold
This parameter sets the ERLE requirement for dis-
crimination between echo and near-end speech by
the supplementary echo suppressor. See the De-
sign Considerations section on Transmit Suppres-
sion for full details.
HHold - Hold in Half-Duplex on Howl
This is a control flag which, if enabled, holds the
system in the half-duplex operation if it were to
howl for any reason and the howl detectors trip and
clear coefficients. The system may transition to
full-duplex if the flag is subsequently cleared.
Reset
A hardware reset, achieved by bringing RST low
for at least 1 µs and then high again, must be ap-
plied after initial power-on.
When RST is held low, the various internal blocks
of the CS6420 are powered down. When RST is
brought high, the oscillator is enabled and approx-
imately 4 ms later, all digital clocks begin operat-
ing. The ADCs and DACs are calibrated and all
internal digital initializations occur. The MCR is
DS205PP2
sampled after the reset timer expires (104 ms after
the rise of RST or sooner if using the early exit de-
scribed below) to determine whether the reset was
warm or cold. After the MCR is initially sampled,
the default (reset) values of the MCR are restored
to it.
Cold reset is a total reset of all the components of
the CS6420. The ADCs and DACs are reset, the
echo canceller memories and registers are all
cleared, and the default settings of the MCR are re-
stored. Cold reset is the default reset mode upon
power up or in the absence of a microcontroller.
Warm reset is like cold reset except that the echo
canceller coefficients and certain key variables are
not cleared, but instead keep their pre-reset value.
This gives the CS6420 a headstart in adapting to its
environment if the echo environment is relatively
stable, assuming a cold reset happened at least once
since power up.
The CS6420 is warm reset by raising the RST pin
high, waiting 4 ms for the digital clocks to start, and
then writing 0111111111111110 (0x7FFE) to the
MCR within 104 ms after RST goes high. If no
control word is sent, the CS6420 will cold reset. If
the control word is sent after the timer has expired,
it is interpreted as a normal control word.
Another special reset option is to exit the 100 ms
reset timer before the 100 ms has elapsed. This is
accomplished by writing a control word to the
MCR with Bit 15 set high. To exit the timer early
in cold reset, write 1000000000000 (0x8000). The
timer may be bypassed and warm reset asserted by
sending
100 ms timer prevents operation until the bias volt-
ages generated on-chip settle, but the startup delay
might be objectionable in some applications.
Clocking
The clock for the converters and DSP is provided
via the clocking pins, CLKI (pin 14) and CLKO
(pin 13). A 20.480 MHz parallel resonant crystal
1111111111111110
(0xFFFE).
CS6420
The
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