W89C940 Datasheet, PDF (11/61 Pages) Winbond – ELANC-PCI (TWISTED-PAIR ETHER-LAN CONTROLLER WITH PCI INTERFACE)

W89C940
File 1
The ELANC-PCI also contains a Serial Network Adapter (SNA), which adapts the Non-Return-to-Zero (NRZ)
used in the core processor and host system to Manchester coded network symbols.
The SNA contains three blocks: a Phase Locked Loop (PLL), a Manchester encoder/decoder, and a collision
decoder, as well as crystal/oscillator logic.
The Manchester encoder/decoder handles code interpretation between NRZ signals and Manchester coded
signals. The PLL locks the receiving signals with an internal voltage control oscillator (VCO) so that network
noise(jitter) can be eliminated before the signals enter the core coprocessor. The collision decoder detects
whether the network is in a collision status.
10BASE-T MAU FUNCTION
TP Transceiver Operation
Transmit Driver
There are two signals for data transmission, TXP and TXN, which connect to the twisted-pair cable via a
transmitter filter and an optional common mode choke.
Smart Squelch
The main function of this block is to determine when valid data are present on the differential receiving inputs
(RXP/RXN). To ensure that impulse noise on the medium will not be taken as a valid datum, this circuit adopts
a combination of amplitude and timing measurements to determine the validity of the input signals. To qualify
incoming data, the smart squelch circuitry monitors the signals for three peaks of alternating polarity that occur
within a 400 nS window. Once this condition has been satisfied, the squelch level is reduced to minimize the
noise effect and the chances of causing premature Start Of Idle (SOI) pulse detection. If the receiver detects
activity on the receive line while packets are being transmitted, incoming data is qualified on five peaks of
alternating polarity so as to prevent false collisions caused by impulse noise. The squelch function returns to its
squelch state under any of the following conditions:
− A normal Start Of Idle (SOI) signal
− An inverted SOI signal
− A missing SOI signal
A missing SOI signal is assumed when no transitions have occurred on the receiver for 175nS after a packet
has arrived. In this case, a normal SOI signal is generated and appended to the data.
Collision Detection
A collision occurs when transmit and receive signals occur simultaneously on the twisted pair cable. Collisions
will not be reported when the device is in link-fail state. The collision signal is also generated when the
transceiver has detected a jabber condition or when the SQE test is being performed.
SQE test
The Signal Quality Error (SQE) test is used to test the collision signaling circuitry in the Twisted Pair
Transceiver module. After each packet transmission, an SQE signal is sent to the SLCT. The SLCT expects this
signal and will flag an error if it does not exist.
Jabber
The jabber timer monitors the transmitter and disables the transmission if the transmitter is active for greater
than 26.2 mS.The jabber will re-enable the transmitter after the SLCT has been idle for at least 420 mS.
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