AM79C875KI AMD (ADVANCED MICRO DEVICES), AM79C875KI Datasheet - Page 21

• Manufacturer Part Number: AM79C875KI
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C875KI

• Lead Free Status / RoHS Status: Not Compliant

Auto-Negotiation and Miscellaneous
Functions
Auto-Negotiation
The object of the Auto-Negotiation function is to deter-
mine the abilities of the devices sharing a link. After ex-
changing abilities, the NetPHY™ 4LP device and
remote link partner device acknowledge each other
and make a choice of which advertised abilities to sup-
port. The Auto-Negotiation function facilitates an or-
dered resolution between exchanged abilities. This
exchange allows both devices at either end of the link
to take maximum advantage of their respective shared
abilities.
The NetPHY™ 4LP device implements the transmit
and receive Auto-Negotiation algorithm as defined in
IEEE 802.3u, Section 28. The Auto-Negotiation algo-
rithm uses a burst of link pulses called Fast Link Pulses
(FLP). The burst of link pulses are spaced between 55
and 140 µs so as to be ignored by the standard
10BASE-T algorithm. The FLP burst conveys informa-
tion about the abilities of the sending device. The
receiver can accept and decode an FLP burst to learn
the abilities of the sending device. The link pulses
transmitted conform to the standard 10BASE-T tem-
plate. The NetPHY™ 4LP device can perform auto-
negotiation with reverse polarity link pulses. The
NetPHY™ 4LP device supports Next Page advertise-
ment.
The NetPHY™ 4LP device uses the Auto-Negotiation
algorithm to select the type connection to be estab-
lished according to the following priority: 100BASE-TX
full duplex, 100BASE-T4, 100BASE-TX half-duplex,
10BASE-T full duplex, 10BASE-T half-duplex. The
device does not support 100BASE-T4 connections.
The Auto-Negotiation algorithm is initiated when one or
the following events occurs: Auto-Negotiation enable
bit is set, or reset, or soft reset, or transition to link fail
state (when Auto-Negotiation enable bit is set), or
Auto-Negotiation restart bit is set. The result of the
Auto-
tus register for the port of interest (Diagnostic Register,
Register 18).
The NetPHY™ 4LP device supports Parallel Detection
for remote legacy devices that do not support the Auto-
Negotiation algorithm. In the case that a 100BASE-TX
only device is connected to the remote end, the Net-
PHY™ 4LP device will see scrambled idle symbols and
establish a 100BASE-TX only connection. If NLPs are
seen, the NetPHY™ 4LP device will establish a
10BASE-T connection.
Loopback Operation
A local loopback and a remote loopback are provided
for diagnostic testing. Local loopback can be achieved
Negotiation process can be read from the sta-
Am79C875
by writing to Register 0, bit 14 (LPBK). Remote loop-
back can be achieved by writing to Register 24, bit 3.
The local loopback routes transmitted data at the out-
put of the NRZ-to-NRZI conversion module back to the
receiving path’s clock and data recovery module for
connection to PCS in 5-bit symbol format. This loop-
back is used to check all the device’s connection at the
5-bit symbol bus side and the operation of the analog
phase locked loop. In the local loopback mode, the SDI
output is forced to high and the TX± outputs are
tri-stated.
The remote loopback routes receiving data at the out-
put of the clock and data recovery module to the trans-
mitting path’s NRZI-to-MLT-3 conversion module. This
loopback is used to check the device’s connection on
the media side and the operation of its internal adaptive
equalizer, digital phase locked loop, and digital wave
shape synthesizer. During the remote loopback mode,
the SDI output is forced to low.
Power Savings Mechanisms
The NetPHY™ 4LP device has three mechanisms for
reducing power: Selectable 1.25:1 transmit transformer
ratio, Unplugged, and Power Down.
Selectable Transformer
The TX outputs can drive either a 1:1 transformer or a
1.25:1 transformer. The latter can be used to reduce
transmit power further. The TP1_1 pin must be pulled
low at reset to select 1.25:1 transformers. The current
at the TX± pins for a 1:1 ratio transformer is 40 mA for
MLT-3 and 100 mA for 10BASE-T. Using the 1.25:1
ratio reduces the current to 32 mA for MLT-3 and 80 mA
for 10BASE-T.
The cost of using the 1.25:1 option is in impedance
coupling. The reflected capacitance is increased by the
square of the ratio of windings (1.25
reflected capacitance on the media side is roughly
1½ times the capacitance on the board. Extra care in
the layout to control capacitance on the board is re-
quired.
Unplugged
The Unplugged feature reduces power consumption
whenever the PHY is operating. The TX output drivers
limit the drive capability if the corresponding receivers
do not detect a link partner within 4 seconds. This pre-
vents “wasted” power. If the receiver detects the ab-
sence of a link partner, the corresponding transmitter is
limited to transmitting normal link pulses. Any energy
detected by the receiver enables full transmit capabili-
ties. A typical situation encountered is that most un-
used ports still consume power. Up to 25% of repeater
and switch ports are unconnected to allow room for fu-
ture expansion. With NetPHY™ 4LP, unconnected
ports have their receiver disabled until energy is de-
tected. The power savings is most notable on uncon-
2
= 1.56). Thus, the
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