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CS6422
Technical Brief
UPGRADING FROM THE CS6420 TO THE CS6422
This document contains information that is useful in The following table summarizes the bit fields that transitioning a system from the CS6420 to the have changed: CS6422. CS6420 CS6422 CS6420 CS6422 CS6422
Performance Differences
The analog and echo cancelling performance of the CS6422 is identical to the CS6420. The CS6422 incorporates a super-set of features and enhanced configuration options.
Reg HD
Reg HDD
Values same
Values same
Default same (Half duplex allowed) same (+18dB) same (0dB) 6dB 6dB 6dB same (39.5/24 ms) same (3dB/s) same (15dB)
RVol TVol THDet RHDet RSThd Taps NseRmp TSThd
RVol TVol THDet RHDet RSThd Taps NseRmp TSThd
-60dB to +30dB -60dB to +30dB 3,5,6dB 3,5,6dB 3,5,6dB
-12dB to +30dB -12dB to +30dB 6,9,12dB 6,9,12dB 6,9,12dB
Board-level Changes
The CS6420 and CS6422 are 100% pin compatible. No board-level changes are necessary (or recommended) for migrating to the CS6422. However, any circuitry added to a CS6420 system to implement an external sidetone can be eliminated (or remain unpopulated) if the internal programmable sidetones on the CS6422 are used.
55.5/--- ms 55.5/8 ms 1.5,3,6dB/s 3,6,12dB/s 9,12,15dB 9,12,15, 18dB
Register Definition Changes
New Register/Feature Additions:
A number of CS6420 register bit fields have been 1) Explicit disable controls AECD and NECD have been added to disable the acoustic and netrenamed and some of the definitions and values work echo cancellers independently. In the have been modified in the CS6422. The register CS6420, the network canceller is disabled by almapping (location and decoding of registers) is locating all the Taps to the AEC. In the CS6422, completely new. the NEC is disabled by setting NECD. The Taps The CS6422 register map provides for 4 bits of adparameter can be set to any allowed value. dress decoding (compared to 3 bits in the case of the CS6420), or 8 independent addresses (bit 0 is al- 2) Auto network path detect. The CS6422 is able to detect when a network path is present or absent ways `0'), 6 of which are implemented. Each regisand can automatically enable or disable the netter contains 12 bits of configuration information. work echo canceller as appropriate, even during Furthermore, all but one of the bit fields reside on a call in progress. To enable this feature, NFNse nibble boundaries, making conversions to and from should be set to a non-zero value (this allows the hexadecimal very convenient. NEC to be disabled if a network path is not detected), and AuNECD should be set to `0' (this For further information, please contact Crystal Product Support at (512) 445-7222 or 1 (800) 888-5016
Cirrus Logic, Inc. Crystal Semiconductor Products Division P.O. Box 17847, Austin, Texas 78760 (512) 445 7222 FAX: (512) 445 7581 http://www.crystal.com
Copyright (c) Cirrus Logic, Inc. 1999 (All Rights Reserved)
JAN `99 DS295TB1 1
CS6422
allows the NEC to be enabled after it has been disabled by NFNse). 3) Transmit Noise Guard. Transmit noise guard is a noise squelch feature that introduces attenuation (set by TSAtt) in the transmit channel when the near-end is silent. This prevents unwanted noise (from a car or other noisy environment) from being transmitted to the far-end listener. Noise guard is enabled by default, and is disabled by setting TSMde to a `1'. 4) Double-talk Attenuation. Double-talk Attenuation introduces a programmable amount of loss into the transmit and/or the receive path during full-duplex double-talk. This feature enhances system stability in hands-free full-duplex to hands-free full-duplex conversations by limiting the gain in the acoustic coupling loop, allowing for higher volume levels at both ends of the connection. Two parameters (TDbtS and RDbtS) control the amount of attenuation that is added to the transmit and receive channels, respectively. Double-talk attenuation is disabled by default (both attenuators are set to 0 dB). The decay rate of the attenuation is configurable through TDSRmp and RDSRmp for the transmit and receive channels respectively. Both of these parameters default to the `slow' setting which provides a decay rate of about 1 second. Most implementations should use the 'normal' setting, which provides a decay rate of about 250 ms. 5) Programmable Sidetones. The parameters ASdt and NSdt allow for a digital path to be created between AO and APO (ASdt) or NO and NI (NSdt). These digital paths are superimposed on the real acoustic or network paths and are canceled by the appropriate echo canceller. In certain environments, most notably the car environment where the acoustic path is weak, inconsistent, or distorted, the presence of a strong linear path can enhance system performance. Both acoustic and network sidetones are disabled by default. 6) Test features. The CS6422 contains a number of features that are useful in the design and debug stages of a system. Separate disable controls (AECD and NECD) allow the acoustic path and the network path to be debugged and tested independently. HwlD and TD allow the howl detector and tone detector to be disabled. APCD and NPCD allow the acoustic and network path change detectors to be disabled, forcing each canceller to train out of a path change rather than training from a cleared state on a major path change. APFD and NPFD allow the pre-emphasis filters on the acoustic and network echo cancellers to be disabled. This enhances results when testing ERLE performance with white noise.
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