CS6403 datasheet(42/54 Pages) CIRRUS

42 / 54 page

SSI

Mode 2 of the CS6403 requires that the far-end in-

put and output are provided to the CS6403 digitally

via the Synchronous Serial Interface (SSI). The ten

pin dual-row stake header J1 presents these signals

for easy access to a DSP serial port. See Figure 6

for pinout.

These signals are still available in Mode 1, however,

SDI will be driven by the MC145480 and care

should be taken to avoid contention on this pin if

anything is connected to the SSI.

Reset

The Reset button is used to reset the CS6403 to

a known state. The reset circuitry is intended to

perform a power-on reset function. The Schmitt-

trigger inverter corrects the sense of the RESET

signal for the CS6403 and debounces the switch.

Figure 7 shows the Reset circuit, as well as, the

EPLD and connected switches.

Algorithm Control

A bank of switches near the digital patch area al-

lows the user some control of the behavior of the

algorithms running on the CS6403. SW6 is la-

belled NORMAL and CLEAR and controls the

state of the coefficients in the echo canceller’s

adaptive filter.

SW2-5 are momentary contact

pushbutton switches which provide volume con-

trol and control of the half-duplex mode of the

CS6403.

In NORMAL mode the signal injected at FE_IN

will come out SPKROUT, be picked up by MI-

CIN, and transmitted to FE_OUT. The signal at

FE_OUT should be echo cancelled, that is, the

signal coupling at the near-end is substantially

attenuated at the far-end output. It will take a

few seconds of far-end speech, with the near-end

being quiet to converge the echo canceller. Until

then, a half-duplex mode is in place to prevent

howling and to hide the echoes present before

the echo canceller is converged.

If SW6 is moved to the CLEAR position, the co-

efficients in the adaptive filter will be cleared,

effectively disabling the echo canceller.

Note

that if the half-duplex mode is enabled (it is by

default), the CS6403 will be held in half-duplex

mode.

If half-duplex is disabled, the signal at

FE_OUT will be whatever is received at MICIN.

In order to disable the half-duplex mode, the

user need only push the HD OFF pushbutton

(SW5).

The four control buttons are momentary contact

buttons which change the state of operation of

the echo-canceller.

The "HD ON" button en-

ables the half-duplex fallback mode of the echo

canceller.

The "HD OFF" button disables the

half-duplex mode. Note that if the echo-cancel-

ler cannot provide enough echo suppression,

howling may occur with the half-duplex mode

disabled. "VOL UP" and "VOL DOWN" control

the output volume of the SPKROUT pins.

Pressing "VOL UP" will increase the volume by

one step and pressing "VOL DOWN" will de-

crease it. Volume may be raised to a level of 0

and down to 41.

GPOUT0 will go high for

125

µs (visible as a flash) if an attempt is made

to go out of the volume range.

The reset state of the CS6403 is half-duplex

mode enabled and volume level of 4.

SSYNC

SCLK

SDI

SDO

+5VD

RP1

47k

Ω

AGND

Figure 6. Synchronous Serial Interface (SSI)

Stake Header

CDB6403

DS192DB3

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