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LAN8187i Datasheet(PDF) 20 Page - SMSC Corporation |
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LAN8187i Datasheet(HTML) 20 Page - SMSC Corporation |
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20 / 78 page  ±15kV ESD Protected MII/RMII 10/100 Ethernet Transceiver with HP Auto-MDIX & flexPWR® Technology Datasheet Revision 1.7 (03-04-11) 20 SMSC LAN8187/LAN8187i DATASHEET 4.2.3 Scrambling Repeated data patterns (especially the IDLE code-group) can have power spectral densities with large narrow-band peaks. Scrambling the data helps eliminate these peaks and spread the signal power more uniformly over the entire channel bandwidth. This uniform spectral density is required by FCC regulations to prevent excessive EMI from being radiated by the physical wiring. The seed for the scrambler is generated from the PHY address, PHYAD[4:0], ensuring that in multiple- PHY applications, such as repeaters or switches, each PHY will have its own scrambler sequence. The scrambler also performs the Parallel In Serial Out conversion (PISO) of the data. 4.2.4 NRZI and MLT3 Encoding The scrambler block passes the 5-bit wide parallel data to the NRZI converter where it becomes a serial 125MHz NRZI data stream. The NRZI is encoded to MLT-3. MLT3 is a tri-level code where a change in the logic level represents a code bit “1” and the logic output remaining at the same level represents a code bit “0”. 4.2.5 100M Transmit Driver The MLT3 data is then passed to the analog transmitter, which drives the differential MLT-3 signal, on outputs TXP and TXN, to the twisted pair media across a 1:1 ratio isolation transformer. The 10Base- T and 100Base-TX signals pass through the same transformer so that common “magnetics” can be used for both. The transmitter drives into the 100 Ω impedance of the CAT-5 cable. Cable termination and impedance matching require external components. 4.2.6 100M Phase Lock Loop (PLL) The 100M PLL locks onto reference clock and generates the 125MHz clock used to drive the 125 MHz logic and the 100Base-Tx Transmitter. 00000 V INVALID, RX_ER if during RX_DV INVALID 00001 V INVALID, RX_ER if during RX_DV INVALID 00010 V INVALID, RX_ER if during RX_DV INVALID 00011 V INVALID, RX_ER if during RX_DV INVALID 00101 V INVALID, RX_ER if during RX_DV INVALID 01000 V INVALID, RX_ER if during RX_DV INVALID 01100 V INVALID, RX_ER if during RX_DV INVALID 10000 V INVALID, RX_ER if during RX_DV INVALID Table 4.1 4B/5B Code Table (continued) CODE GROUP SYM RECEIVER INTERPRETATION TRANSMITTER INTERPRETATION |
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