LAN9211 datasheet(71/147 Pages) SMSC

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High-Performance Small Form Factor Single-Chip Ethernet Controller with HP Auto-MDIX Support

Datasheet

SMSC LAN9211

Revision 2.9 (03-01-12)

DATASHEET

clock. This is used to Manchester encode the NRZ data stream. When no data is being transmitted

(TX_EN is low), the TX10M block outputs Normal Link Pulses (NLPs) to maintain communications with

the remote link partner.

4.4.3

10M Transmit Drivers

The Manchester encoded data is sent to the analog transmitter where it is shaped and filtered before

being driven out as a differential signal across the TXP and TXN outputs.

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

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.

4.6

Auto-negotiation

The purpose of the Auto-negotiation function is to automatically configure the PHY to the optimum link

parameters based on the capabilities of its link partner. Auto-negotiation is a mechanism for

exchanging configuration information between two link-partners and automatically selecting the highest

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