AM79C875KI AMD (ADVANCED MICRO DEVICES), AM79C875KI Datasheet - Page 19

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

Specifications of AM79C875KI

• Lead Free Status / RoHS Status: Not Compliant

signal on the first NLP. It locks the polarity correction
circuitry after the reception of two consecutive packets.
The state of the polarity correction circuitry is locked as
long as link is established. This function is only avail-
able in 10BASE-T mode.
Far-End Fault Indication (FEFI)
Auto-Negotiation provides a remote fault capability for
d e t e c t i n g a n a s y m m e t r i c l i n k f a i l u r e . S i n c e
100BASE-FX systems do not use Auto-Negotiation, an
alternative, in-band signaling scheme is used to signal
remote fault conditions. This scheme, Far End Fault In-
dication, relies on the characteristics of the quiescent
state, a continuous IDLE stream. The IDLE stream is a
continuous stream of logic ones followed by one logic
zero, with the pattern repeated at least 3 times.
A Far-End Fault will be signaled under the following
three conditions: (1) When no activity is received from
the link partner, since this can indicate a broken receive
wire, (2) When the clock recovery circuit detects a
receive signal error or PLL lock error, (3) When man-
agement entity sets the transmit Far-end fault bit
(Register 24, bit 7).
The Far-End fault mechanism defaults to enabled in
100BASE-FX mode and disabled in 100BASE-TX and
10BASE-T modes, and may be controlled by software
after reset.
MLT-3
This block is responsible for converting the NRZI data
stream from the PDX block to the MLT-3 encoded data
stream. The effect of MLT-3 is the reduction of energy
on the copper media (TX or FX cable) in the critical
frequency range of 1 MHz to 100 MHz. The receive
section of this block is responsible for equalizing and
amplifying the received data stream and link detection.
The adaptive equalizer compensates for the amplitude
and phase distortion due to the cable.
MLT-3 is a tri-level signal. All transitions are between
0 V and +1 V or 0 V and -1 V. A transition has a logical
value of 1 and a lack of a transition has a logical value
of 0. The benefit of MLT-3 is that it reduces the maxi-
mum frequency over the data line. The bit rate of TX
data is 125 Mbps. The maximum frequency (using
NRZI) is half of 62.5 MHz. MLT-3 reduces the maxi-
mum frequency to 31.25 MHz.
A data signal stream following MLT-3 rules is illustrated
in Figure 6. The data stream is 1010101.
Am79C875
The TX± drivers convert the NRZI serial output to
MLT-3 format. The RX± receivers convert the received
MLT-3 signals to NRZI. The transmit and receive sig-
nals will be compliant with IEEE 802.3u, Section 25.
The required signals (MLT-3) are described in detail in
ANSI X3.263:1995 TP-PMD Revision 2.2 (1995).
The NetPHY™ 4LP device provides on-chip filtering.
External filters are not required for either the transmit or
receive signals.
The TX± pins can be connected to the media via either
a 1:1 transformer or a 1.25:1 transformer. The 1.25:1
ratio provides a 20% transmit power savings over the
1:1 ratio. Refer to Figure 7.
Adaptive Equalizer
The NetPHY™ 4LP device is designed for the maxi-
mum of 140 meter UTP-5 cable. A 140-meter UTP-5
cable attenuates the signal by 32 dB at 100 MHz which
far exceed the cable plant attenuation (24-26 dB) de-
fined by TP-PMD.
The amplitude and phase distortion from cable causes
inter-symbol interference (ISI) which makes clock and
data recovery impossible. Adaptive equalization is
done by closely matching the characteristics of the
twisted-pair cable. This is a variable equalizer which
changes equalizer frequency response in accordance
with cable length. The cable length is estimated based
on comparisons of incoming signal strength against
some known cable characteristics. The equalizer tunes
itself automatically to the any cable length to compen-
sate for the amplitude and phase distortion incurred
from the cable.
Baseline Wander Compensation
The 100BASE-TX data stream is not always DC bal-
anced. The media, with transformer and common
MLT-3
1
8 ns
Figure 6. MLT-3 Waveform
0
1
0
1
0
22236G-8
1
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