KS8995XA Ver la hoja de datos (PDF) - Micrel

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Fabricante

KS8995XA

Integrated 5-Port 10/100 QoS Switch

Micrel 

KS8995XA

Micrel, Inc.

100BASE-FX Signal Detection

The physical port runs in 100BASE-FX mode if FXSDx >0.6V for ports 4 and 5 only. This signal is internally referenced to

1.25V.The fiber module interface should be set by a voltage divider such that FXSDx ‘H’ is above this 1.25V reference,

indicating signal detect, and FXSDx ‘L’ is below the 1.25V reference to indicate no signal. When FXSDx is below 0.6V then

100BASE-FX mode is disabled.

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 1’s followed by a zero in the idle period between frames. The

far end fault may be disabled through register settings.

10BASE-T Transmit

The output 10BASE-T 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 buffer 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 clock signal and NRZ data. A

squelch circuit rejects signals with levels less than 400mV or with short pulsewidths 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 KS8995XA decodes a data frame. The receiver clock is maintained active during idle periods in between data

reception.

Power Management

The KS8995XA features a per port power down mode. To save power the user can power down ports that are not in use by

setting port control registers or MII control registers. In addition, it also supports full chip power down mode. When activated,

the entire chip will be shutdown.

MDI/MDI-X Auto Crossover

The KS8995XA supports MDI/MDI-X auto crossover. This facilitates the use of either a straight connection CAT-5 cable or a

crossover CAT-5 cable. The auto-sense function will detect remote transmit and receive pairs, and correctly assign the transmit

and receive pairs from the Micrel device. This can be highly useful when end users are unaware of cable types and can also

save on an additional uplink configuration connection. The auto crossover feature may be disabled through the port control

registers.

Auto-Negotiation

The KS8995XA conforms to the auto-negotiation protocol as described by the 802.3 committee. Auto-negotiation allows

unshielded twisted pair (UTP) link partners to select the best common mode of operation. In auto-negotiation the link partners

advertise capabilities across the link to each other. If auto-negotiation is not supported or the link partner to the KS8995XA

is forced to bypass auto-negotiation, then the mode is set by observing the signal at the receiver. This is known as parallel mode

because while the transmitter is sending auto-negotiation advertisements, the receiver is listening for advertisements or a fixed

signal protocol.

The flow for the link set up is depicted in Figure 4.

M9999-051305

20

May 2005

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