VT6103 datasheet(31/46 Pages) VIA

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VT6103 - Fast Ethernet 10 / 100 PHY / Transceiver

Revision 1.1 April 15, 2002

-25-

Functional Description

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Miscellaneous Functions

Smart Squelch

Smart squelch is responsible for determining when valid data

is present on the differential receive inputs (TPRD+/-). The

VT6103 implements an intelligent receive squelch algorithm

to ensure that impulse noise on the receive inputs will not be

mistaken for a valid signal.

Smart squelch operation is

independent of the 10Base-T operational mode. The squelch

circuitry employs a combination of amplitude and timing

measurements (as specified in the IEEE 802.3 10Base-T

standard) to determine the validity of data on the twisted pair

inputs (refer to IEEE802.3).

The signal at the Start of Packet is checked by the smart

squelch circuit and any pulses not exceeding the squelch level

(either positive or negative, depending upon polarity) will be

rejected. Once this first squelch level is overcome correctly,

the opposite squelch level must then be exceeded within 150

ns. Finally the signal must exceed the original squelch level

within a further 150 ns to ensure that the input waveform will

not be rejected. The checking procedure results in the loss of

typically three preamble bits at the beginning of each packet.

Only after all these conditions have been satisfied will a

control signal be generated to indicate to the remainder of the

circuitry that valid data is present. At this time, the smart

squelch circuitry is reset.

Valid data is considered to be

present until squelch level has not been generated for a time

longer than 150ns, indicating End of Packet. Once good data

has been detected the squelch levels are reduced to minimize

the effect of noise causing premature End of Packet detection.

The receive squelch threshold level can be lowered for use in

longer cable or STP applications. This is achieved by setting

the F10LSS bit in the PHYCONFIG register (bit 7, register

10h).

Collision Detection

For Half Duplex, a 10Base-T collision is detected when the

receive and transmit channels are active simultaneously.

Collisions are reported by the COL signal on the MII. If the

ENDEC is transmitting when a collision is detected, the

collision is not reported until seven bits have been received

while in the collision state. This prevents a collision from

being reported incorrectly due to noise on the network. The

COL signal remains set for the duration of the collision. If the

ENDEC is receiving when a collision is detected, it is reported

immediately (through the COL signal).

When heartbeat is

enabled, approximately 1 ms after the transmission of each

packet, a Signal Quality Error (SQE) signal of approximately

10 bit times is generated (internally) to indicate successful

transmission. SQE is reported as a pulse on the COL signal of

the MII.

Carrier Sense

Carrier Sense (CRS) may be asserted due to receive activity

once valid data is detected via the smart squelch function. For

10 Mb/s Half Duplex operation, CRS is asserted during either

packet transmission or reception. For 10 Mb/s Full Duplex

operation, CRS is asserted only due to receive activity. CRS

is deasserted following an end of packet. In Repeater mode,

CRS is only asserted due to receive activity.

Normal Link Pulse Detection / Generation

The link pulse generator produces pulses as defined in the

IEEE 802.3 10Base-T standard. Each link pulse is nominally

100 ns in duration and is transmitted every 16 ms ± 8 ms, in

the absence of transmit data. Link pulse is used to check the

integrity of the connection with the remote end. If valid link

pulses are not received, the link detector disables the 10Base-

T twisted pair trans-mitter, receiver and collision detection

functions. When the link integrity function is disabled, the

10Base-T transceiver will operate regardless of the presence

of link pulses.

VT6103 Datasheet(PDF) 31 Page - VIA Technologies, Inc.

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