AM79C873 datasheet(17/44 Pages) AMD

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Am79C873

PRELIMINARY

cause serious under-compensation for longer length

cables. Therefore, the compensation or equalization

must be adaptive to ensure proper conditioning of the

received signal independent of the cable length.

PECL Receiver

The PECL receiver accepts PECL signal-level data

from the FX Optical Module and presents it to the Clock

Recovery Module.

MLT-3-to-NRZI Decoder

The NetPHY-1 device decodes the MLT-3 information

from the Digital Adaptive Equalizer into NRZI data. The

relationship between NRZI and MLT-3 data is shown in

Figure 4.

Clock Recovery Module

The Clock Recovery Module accepts NRZI data from

the MLT-3-to-NRZI decoder or the PECL Receiver. The

Clock Recovery Module locks onto the data stream and

extracts the 125 MHz reference clock. The extracted

and synchronized clock and data are presented to the

NRZI-to-NRZ Decoder.

NRZI-to-NRZ Decoder

The transmit data stream is required to be NRZI en-

coded in for compatibility with 100BASE transmission

over. 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.

Serial-to-Parallel Converter

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.

Descrambler

Because of the scrambling process required to control

the radiated emissions of transmit data streams, the re-

ceiver 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.

Note: The scrambler is bypassed for 100BASE-FX

operation.

Code Group Alignment

The Code Group Alignment block receives unaligned

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.

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 two 5-bit code

groups received are the start-of-frame delimiter (J/K

symbols). The J/K symbol pair is stripped and two nib-

bles of preamble pattern are substituted. The last two

code groups are the end-of-frame delimiter (T/R sym-

bols).The T/R symbol pair is also stripped from the nib-

ble presented to the Reconciliation layer.

10BASE-T Operation

The 10BASE-T transceiver is IEEE 802.3u compliant.

When the NetPHY-1 device is operating in 10BASE-T

mode, the coding scheme is Manchester. Data pro-

cessed 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 nib-

ble format for presentation to the MII interface.

Collision Detection

For Half Duplex operation, a collision is detected when

the transmit and receive channels are active simulta-

neously. When a collision has been detected, it will be

reported by the COL signal on the MII interface. Colli-

sion detection is disabled in Full Duplex operation.

Carrier Sense

Carrier Sense (CRS) is asserted in Half Duplex oper-

ation during transmission or reception of data. During

Full Duplex mode, CRS is asser ted only during

receive operations.

Auto-Negotiation

The objective of Auto-Negotiation is to provide a means

to exchange information between segment linked de-

vices and to automatically conﬁgure both devices to

take maximum advantage of their abilities. It is impor-

tant 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, acknowl-

edge the receipt and understanding of common modes

of operation, and to reject un-shared modes of opera-

tion. 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 prede-

termined priority resolution function.

Auto-Negotiation also provides a parallel detection

function for devices that do not support the Auto-Nego-

tiation feature. During Parallel detection there is no ex-

change of conﬁguration information, instead, the

receive signal is examined. If it is discovered that the

signal matches a technology that the receiving device

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