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DM9006 Datasheet(PDF) 67 Page - Davicom Semiconductor, Inc. |
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DM9006 Datasheet(HTML) 67 Page - Davicom Semiconductor, Inc. |
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67 / 76 page 
DM9006 2-port Switch with Processor Interface Preliminary datasheet 67 DM9006-13-DS-P01 September 1, 2009 9.3.2 100Base-TX Receiver The 100Base-TX receiver contains several function blocks that convert the scrambled 125Mb/s serial data to synchronous 4-bit nibble data. The receive section contains the following functional blocks: - Signal Detect - Digital Adaptive Equalization - MLT-3 to Binary Decoder - Clock Recovery Module - NRZI to NRZ Decoder - Serial to Parallel - Descrambler - Code Group Alignment - 4B5B Decoder 9.3.2.1 Signal Detect The signal detects function meets the specifications mandated by the ANSI XT12 TP-PMD 100Base-TX standards for both voltage thresholds and timing parameters. 9.3.2.2 Adaptive Equalization When transmitting data over copper twisted pair cable at high speed, attenuation based on frequency becomes a concern. In high speed twisted pair signaling, the frequency content of the transmitted signal can vary greatly during normal operation based on the randomness of the scrambled data stream. This variation in signal attenuation, caused by frequency variations, must be compensated for to ensure the integrity of the received data. In order to ensure quality transmission when employing MLT-3 encoding, the compensation must be able to adapt to various cable lengths and cable types depending on the installed environment. The selection of long cable lengths for a given implementation requires significant compensation, which will be over-killed in a situation that includes shorter, less attenuating cable lengths. Conversely, the selection of short or intermediate cable lengths requiring less compensation will cause serious under-compensation for longer length cables. Therefore, the compensation or equalization must be adaptive to ensure proper conditioning of the received signal independent of the cable length. 9.3.2.3 MLT-3 to NRZI Decoder The DM9006 decodes the MLT-3 information from the Digital Adaptive Equalizer into NRZI data. 9.3.2.4 Clock Recovery Module The Clock Recovery Module accepts NRZI data from the MLT-3 to NRZI decoder. The Clock Recovery Module locks onto the data stream and extracts the 125 MHz reference clock. The extracted and synchronized clock and data are presented to the NRZI to NRZ decoder. 9.3.2.5 NRZI to NRZ The transmit data stream is required to be NRZI encoded for compatibility with the TP-PMD standard for 100Base-TX transmission over Category-5 unshielded twisted pair cable. This conversion process must be reversed on the receive end. The NRZI to NRZ decoder receives the NRZI data stream from the Clock Recovery Module and converts it to a NRZ data stream to be presented to the Serial to Parallel conversion block. 9.3.2.6 Serial to Parallel The Serial to Parallel Converter receives a serial data stream from the NRZI to NRZ converter. It converts the data stream to parallel data to be presented to the descrambler. 9.3.2.7 Descrambler Because of the scrambling process requires to control the radiated emissions of transmit data streams, the receiver must descramble the receive data streams. The descrambler receives scrambled parallel data streams from the Serial to Parallel converter, and it descrambles the data streams, and presents the data streams to the Code Group alignment block. |
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