AM79C873 Advanced Micro Devices, AM79C873 Datasheet - Page 17

• Manufacturer Part Number: AM79C873
• Description: NetPHY -1 10/100 Mbps Ethernet Physical Layer Single-Chip Transceiver with 100BASE-FX Support
• Manufacturer: Advanced Micro Devices

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.
P R E L I M I N A R Y
Am79C873
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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