Davicom DM9000 Manual
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DM9000ISA to Ethernet MAC Controller with Integrated 10/100 PHY34 FinalVersion: DM9000-DS-F02June 26, 20029.6 100Base-TX ReceiverThe 100Base-TX receiver contains several functionblocks that convert the scrambled 125Mb/s serial datato synchronous 4-bit nibble data that is then providedto the MII.The receive section contains the following functionalblocks:- 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 Decoder9.6.1 Signal DetectThe signal detect function meets the specificationsmandated by the ANSI XT12 TP-PMD 100Base-TXstandards for both voltage thresholds and timingparameters.9.6.2 Adaptive EqualizationWhen transmitting data over copper twisted pair cableat high speed, attenuation based on frequencybecomes a concern. In high speed twisted pairsignaling, the frequency content of the transmittedsignal can vary greatly during normal operation basedon the randomness of the scrambled data stream.This variation in signal attenuation, caused byfrequency variations, must be compensated for toensure the integrity of the received data. In order toensure quality transmission when employing MLT-3encoding, the compensation must be able to adapt tovarious cable lengths and cable types depending onthe installed environment. The selection of long cablelengths for a given implementation requires significantcompensation, which will be over-killed in a situationthat includes shorter, less attenuating cable lengths.Conversely, the selection of short or intermediatecable lengths requiring less compensation will causeserious under-compensation for longer length cables.Therefore, the compensation or equalization must beadaptive to ensure proper conditioning of the receivedsignal independent of the cable length.9.6.3 MLT-3 to NRZI DecoderThe DM9000 decodes the MLT-3 information from theDigital Adaptive Equalizer into NRZI data. Therelationship between NRZI and MLT-3 data is shownin figure 4.9.6.4 Clock Recovery ModuleThe Clock Recovery Module accepts NRZI data fromthe MLT-3 to NRZI decoder. The Clock RecoveryModule locks onto the data stream and extracts the1 2 5 M h z r e f e r e n c e c l o c k . T h e e x t r a c t e d a n dsynchronized clock and data are presented to theNRZI to NRZ decoder.9.6.5 NRZI to NRZThe transmit data stream is required to be NRZIencoded for compatibility with the TP-PMD standardfor 100Base-TX transmission over Category-5unshielded twisted pair cable. This conversionprocess must be reversed on the receive end. TheNRZI to NRZ decoder, receives the NRZI data streamfrom the Clock Recovery Module and converts it to aNRZ data stream to be presented to the Serial toParallel conversion block.9.6.6 Serial to ParallelThe Serial to Parallel Converter receives a serialdata stream from the NRZI to NRZ converter. Itconverts the data stream to parallel data to bepresented to the descrambler.9.6.7 DescramblerBecause of the scrambling process requires to controlthe radiated emissions of transmit data streams, thereceiver must descramble the receive data streams.The descrambler receives scrambled parallel datastreams from the Serial to Parallel converter, and itdescrambles the data streams, and presents the datastreams to the Code Group alignment block. |
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