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KSZ8765CLXCC View Datasheet(PDF) - Micrel

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KSZ8765CLXCC Datasheet PDF : 153 Pages
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Micrel, Inc.
KSZ8765CLX
Scrambler/Descrambler (100BASE-TX Only)
The purpose of the scrambler is to spread the power spectrum of the signal in order to reduce EMI and baseline wander.
The data is scrambled through the use of an 11-bit wide linear feedback shift register (LFSR). This can generate a 2047-
bit non-repetitive sequence. The receiver will then descramble the incoming data stream with the same sequence at the
transmitter.
100BASE-FX Operation
100BASE-FX operation is very similar to 100BASE-TX operation except that the scrambler/descrambler and MLT3
encoder/decoder are bypassed on transmission and reception. In this mode, the auto-negotiation feature is bypassed
because there is no standard that supports fiber auto-negotiation regardless auto-negotiation to be enabled or disabled.
100BASE-FX Signal Detection
The physical port runs in 100BASE-FX fiber mode for the Port 1 and Port 2 of the KSZ8765CLX. This signal is internally
referenced to 1.7V. The fiber module interface should be set by a voltage divider such that FXSDx ‘H’ is above this 1.8V
reference, indicating signal detect, and FXSDx ‘L’ is below the 1.7V reference to indicate no signal. There is no auto-
negotiation for 100BASE-FX mode, the ports must be forced to either 100/full-duplex or 100/half-duplex for the fiber ports.
100BASE-FX Far End Fault
Far end fault occurs when the signal detection is logically false from the receive fiber module. When this occurs, the
transmission side signals the other end of the link by sending 84 ones followed by a zero in the idle period between
frames.
10BASE-T Transmit
The 10BASE-T output driver is incorporated into the 100BASE-T driver to allow transmission with the same magnetics.
They are internally wave-shaped and pre-emphasized into outputs with a typical 2.3V amplitude. The harmonic contents
are at least 27dB below the fundamental when driven by an all-ones Manchester-encoded signal.
10BASE-T Receive
On the receive side, input buffers and level-detecting squelch circuits are employed. A differential input receiver circuit
and a PLL perform the decoding function. The Manchester-encoded data stream is separated into a clock signal and NRZ
data. A squelch circuit rejects signals with levels less than 400mV or with short pulse-widths in order to prevent noises at
the RXP or RXM input from falsely triggering the decoder. When the input exceeds the squelch limit, the PLL locks onto
the incoming signal and the KSZ8765CLX decodes a data frame. The receiver clock is maintained active during idle
periods in between data reception.
MDI/MDI-X Auto Crossover
To eliminate the need for crossover cables between similar devices, the KSZ8765CLX supports HP Auto-MDI/MDI-X and
IEEE 802.3u standard MDI/MDI-X auto crossover. HP Auto-MDI/MDI-X is the default.
The auto-sense function detects remote transmit and receive pairs and correctly assigns transmit and receive pairs for the
KSZ8765CLX device. This feature is extremely useful when end users are unaware of cable types, and also, saves on an
additional uplink configuration connection. The auto-crossover feature can be disabled through the Port control registers,
or MIIM PHY registers. The IEEE 802.3u standard MDI and MDI-X definitions are in the table below.
Table 1. MDI/MDI-X Pin Definitions
MDI
RJ-45 Pins
1
2
3
6
July 23, 2014
Signals
TD+
TD-
RD+
RD-
RJ-45 Pins
1
2
3
6
MDI-X
Signals
RD+
RD-
TD+
TD-
21
Revision 1.0
 

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