LAN83C185_03 Datasheet, PDF (25/65 Pages) SMSC Corporation – High Performance Single Chip Low Power 10/100 Ethernet Physical Layer Transceiver

High Performance Single Chip Low Power 10/100 Ethernet Physical Layer Transceiver (PHY)
Datasheet
4.5
10Base-T Receive
The 10Base-T receiver gets the Manchester- encoded analog signal from the cable via the magnetics.
It recovers the receive clock from the signal and uses this clock to recover the NRZI data stream. This
10M serial data is converted to 4-bit data nibbles which are passed to the controller across the MII at
a rate of 2.5MHz.
This 10M receiver uses the following blocks:
■ Filter and SQUELCH (analog)
■ 10M PLL (analog)
■ RX 10M (digital)
■ MII (digital)
4.5.1 10M Receive Input and Squelch
The Manchester signal from the cable is fed into the PHY (on inputs RXP and RXN) via 1:1 ratio
magnetics. It is first filtered to reduce any out-of-band noise. It then passes through a SQUELCH
circuit. The SQUELCH is a set of amplitude and timing comparators that normally reject differential
voltage levels below 300mV and detect and recognize differential voltages above 585mV.
4.5.2 Manchester Decoding
The output of the SQUELCH goes to the RX10M block where it is validated as Manchester encoded
data. The polarity of the signal is also checked. If the polarity is reversed (local RXP is connected to
RXN of the remote partner and vice versa), then this is identified and corrected. The reversed condition
is indicated by the flag “XPOL“, bit 4 in register 27. The 10M PLL is locked onto the received
Manchester signal and from this, generates the received 20MHz clock. Using this clock, the
Manchester encoded data is extracted and converted to a 10MHz NRZI data stream. It is then
converted from serial to 4-bit wide parallel data.
The RX10M block also detects valid 10Base-T IDLE signals - Normal Link Pulses (NLPs) - to maintain
the link.
4.5.3 10M Receive Data across the MII
The 4 bit data nibbles are sent to the MII block. In MII mode, these data nibbles are valid on the rising
edge of the 2.5 MHz RX_CLK.
4.5.4 Jabber detection
Jabber is a condition in which a station transmits for a period of time longer than the maximum
permissible packet length, usually due to a fault condition, that results in holding the TX_EN input for
a long period. Special logic is used to detect the jabber state and abort the transmission to the line,
within 45ms. Once TX_EN is deasserted, the logic resets the jabber condition.
Bit 1.1 indicates that a jabber condition was detected.
4.6
MAC Interface
The MII (Media Independent Interface) block is responsible for the communication with the controller.
Special sets of hand-shake signals are used to indicate that valid received/transmitted data is present
on the 4 bit receive/transmit bus.
SMSC LAN83C185
17
DATASHEET
Rev. 0.6 (12-12-03)