DM9161 datasheet(18/47 Pages) ETC

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DM9161

10/100 Mbps Fast Ethernet Physical Layer Single Chip Transceiver

Final

Version: DM9161-DS-F02

May 10,2002

7.2.2.4 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 125Mhz reference

clock. The extracted and synchronized clock and data are

presented to the NRZI to NRZ Decoder.

7.2.2.5 NRZI to NRZ

The transmit data stream is required to be NRZI encoded in

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.

7.2.2.6 Serial to Parallel

The Serial to Parallel Converter receives a serial data

stream from the NRZI to NRZ converter, and converts

the data stream to parallel data to be presented to the

descrambler.

7.2.2.7 Descrambler

Because 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, descrambles the data

streams, and presents the data streams to the Code Group

alignment block.

7.2.2.8 Code Group Alignment

The Code Group Alignment block receives un-aligned

5B data from the descrambler and converts it into 5B

code group data. Code Group Alignment occurs after

the J/K is detected, and subsequent data is aligned on

a fixed boundary.

7.2.2.9 4B5B Decoder

The 4B5B Decoder functions as a look-up table that

translates incoming 5B code groups into 4B (Nibble) data.

When receiving a frame, the first 2 5-bit code groups

received are the start-of-frame delimiter (J/K symbols). The

J/K symbol pair is stripped and two nibbles of preamble

pattern are substituted. The last two code groups are the

end-of-frame delimiter (T/R symbols).

The T/R symbol pair is also stripped from the nibble

presented to the Reconciliation layer.

7.2.3 10Base-T Operation

The 10Base-T transceiver is IEEE 802.3u compliant. When

the DM9161 is operating in 10Base-T mode, the coding

scheme is Manchester. Data processed for transmit is

presented to the MII interface in nibble format, converted to a

serial bit stream, then Manchester encoded. When receiving,

the Manchester encoded bit stream is decoded and

converted into nibble format for presentation to the MII

interface.

7.2.4 Collision Detection

For half-duplex operation, a collision is detected when the

transmit and receive channels are active simultaneously.

When a collision has been detected, it will be reported by the

COL signal on the MII interface. Collision detection is

disabled in Full Duplex operation.

7.2.5 Carrier Sense

Carrier Sense (CRS) is asserted in half-duplex operation

during transmission or reception of data. During full-duplex

mode, CRS is asserted only during receive operations.

7.2.6 Auto-Negotiation

The objective of Auto-negotiation is to provide a means to

exchange information between segment linked devices and

to automatically configure both devices to take maximum

advantage of their abilities. It is important to note that Auto-

negotiation does not test the link segment characteristics.

The Auto-Negotiation function provides a means for a device

to advertise supported modes of operation to a remote link

partner, acknowledge the receipt and understanding of

common modes of operation, and to reject un-shared

modes of operation. This allows devices on both ends of a

segment to establish a link at the best common mode of

operation. If more than one common mode exists between

the two devices, a mechanism is provided to allow the

devices to resolve to a single mode of operation using a

predetermined priority resolution function.

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