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Integrated Mixed-Signal Solutions
SPDIF Auto Detection for STAC9750/51, STAC9752/53 STAC9766/67 and STAC9758/59
SigmaTel Application Note
Version 1.1
2-AN012-1.1-102202
Copyright (c) 2002 SigmaTel, Inc. All rights reserved. All contents of this document are protected by copyright law and may not be reproduced without the express written consent of SigmaTel, Inc. SigmaTel, the SigmaTel logo, and combinations thereof are registered trademarks and D-Major and C-Major are trademarks of SigmaTel, Inc. Other product names used in this publication are for identification purposes only and may be trademarks or registered trademarks of their respective companies. The contents of this document are provided in connection with SigmaTel, Inc. products. SigmaTel, Inc. has made best efforts to ensure that the information contained herein is accurate and reliable. However, SigmaTel, Inc. makes no warranties, express or implied, as to the accuracy or completeness of the contents of this publication and is providing this publication "AS IS". SigmaTel, Inc. reserves the right to make changes to specifications and product descriptions at any time without notice, and to discontinue or make changes to its products at any time without notice. SigmaTel, Inc. does not assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential, or incidential damages.
SPDIF Auto Detection for STAC9750/51, STAC9752/53 STAC9766/67 and STAC9758/59
OVERVIEW
With the introduction of SPDIF support in the AC'97 revision 2.2 specification (also is included in revision 2.3), many motherboard designs have taken advantage of the cost effective SPDIF support of SigmaTel codecs. While AC'97 describes a method for disabling the SPDIF output, there are a few design rules that can optimize a design when using a SigmaTel codec.
SCOPE
The recommendations and guidelines outlines in this application note apply to all revisions of the STAC9750/51, the STAC9752/53, the STAC9766/67 and the STAC9758.
SPDIF NOT IMPLEMENTED
If SPDIF is not implemented at all in the design, it is important to disable the SPDIF function by forcing pin 48 (SPDIF_OUT) to a high value with a resistor connected to the digital supply. Although it is not necessary to disable the SPDIF function for electrical reasons, disabling the function by pulling pin 48 high will alert the driver that, although the part is capable of supporting SPDIF, the board does not implement SPDIF.
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2-AN012-1.1-102202
SPDIF Auto Detection for STAC9750/51, STAC9752/53 STAC9766/67 and STAC9758/59
SPDIF IMPLEMENTED
When SPDIF is always used, it is necessary to ensure that the state of pin 48 is low during reset. Usually the termination resistors used in a consumer coaxial implementation are sufficient, but some optical transmitters will cause this line to "float" to a high value unless a 110K resistor to ground is used. Current revisions of the STAC9750/51, STAC9752/53, STAC9766/67 and the STAC9758/59 do not have an internal pull-down resistor.
Data sheet, Reference Designs, and additional information are available at www.sigmatel.com.
2-AN012-1.1-102202
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