NWK939
FUNCTIONAL DESCRIPTION
TX10 Latency
TheNWK939hasthreeoperatingmodes:10BASE-Tmode,
100BASE-TX mode and LOW-POWER mode. The modes are
selected by the N10/100 and LPWR_N pins.The Control block
isdesignedtomanagethesemodesbystartingandstoppingthe
two transceivers in a well-controlled manner such that no
spurious signals are output on either the symbol or twisted-pair
interfaces. Furthermore, it continuously monitors the behaviour
of the transceivers and takes corrective action if a fault is
detected.
When connected to appropriate magnetics the latency
through the TX10 path is less than 1BT (100ns) for data
transmissions. This timing is measured from the falling edge of
TXC to the output of the transmit magnetics. The TX10 path will
not transmit the first two Manchester encoded bits of a data
transmission, as permitted by the 802.3 Standard.
RX10 Filter & RX10 Signal Detect
These blocks work in unison to remove noise and to block
signals that do not achieve the voltage levels specified in 802.3.
Signals that do not achieve the required level are not sampled
in the Clock Recovery block and are not passed to the DAT10/
SDT10 and TP_RDP/TP_RDM outputs.
25MHz REFERENCE CLOCK
TheNWK939requiresa25MHz+/-100ppmtimingreference
for 802.3 compliant operation. This may be supplied either from
the integrated oscillator or from an external source. When the
integratedoscillatorisused,asuitablecrystalmustbeconnected
across the XTAL1 & XTAL2 pins (see “External Components”).
Whenanexternalsourceisused,itmustbeinputtotheREFCLK
pinandXTAL1mustbetiedhigh. XTAL2mustbeunconnected.
RX10 Clock Recovery
The RX10 Clock Recovery employs a digital delay line
controlled by the 100MHz Synthesizer DLL to derive a sampling
clock from the incoming signal. The recovered clock runs at
twicethedatarate(nominally20MHz).Whenasignalisreceived
fromtheSignalDetectblock,SDT10isassertedandfallingRXC
is used to strobe Link Pulses and Manchester encoded serial
data out on DAT10 and TP_RDP/TP_RDM. When no signal is
being received, SDT10 is deasserted, RXC is driven from the
20MHztransmitclock,DAT10isheldlowandTP_RDP/TP_RDM
is driven to the zero state (see “DC Electrical Characteristics”).
10BASE-T OPERATION
In 10BASE-T mode Manchester encoded serial data is
loaded from the TP_TDP input, processed through the TX10
Path and output on the TXOP/TXON differential output for
transmission through 1:1 magnetics and onto the twisted-pair.
The incoming signal received from the magnetics into the
RXIP/RXIN differential input is processed through the RX10
Path. Received data is output serially on 2 interfaces. The
DAT10 & SDT10 signals form a Mitel Semiconductor-specific
interface for connection to the NWK936 PCS device. For NIC
controllers that have in-built 10BASE-T receivers, the received
signal is also provided on the TP_RDP/TP_RDM differential
output. The TX10 & RX10 paths are disabled when the device
is not in 10BASE-T mode.
RX10 Latency
When connected to appropriate magnetics the latency
through the RX10 path is less than 1BT (100ns). This timing is
measured from the input of the receive magnetics to the falling
edgeofRXC.TheRX10pathmayignoreuptothreeManchester
encoded bits at the start of data reception (802.3 allows up to 5
bits) and the first bit forwarded to TP_RDP/TP_RDM may have
timing violations (802.3 allows 1 bit).
100MHz Synthesizer
This synthesizer employs a delay-locked loop (DLL) to
generate a 100MHz timing reference from the 25MHz reference
clock.This100MHzreferenceisusedbythe10BASE-Ttransmit
and receive functions and is divided by 5 to provide a 20MHz
data strobe on TXC. The synthesizer is disabled when not in
10BASE-T mode.
100BASE-TX OPERATION
In 100BASE-TX mode 5-bit NRZ symbols are loaded from
theTDATbus,processedthroughtheTX100Pathandoutputon
theTXOP/TXONdifferentialoutputfortransmissionthroughthe
1:1 magnetics and onto the twisted-pair.
The incoming signal received from the magnetics into the
RXIP/RXIN differential input is processed through the RX100
Pathandoutputin5-bitparallelNRZformontheRDATbus. The
TX100 path is disabled when not in 100BASE-TX mode and,
with the exception of the RX100 Signal Detect, the RX100
Receive Path is disabled when not in 100BASE-TX mode.
TX10 Pulse Shaper & Filter
This block loads Link Pulses and Manchester encoded
serial data from the TP_TDP input on the falling edge of TXC.
This input may be connected directly to the TP_TDP output of
the DEC21143 and similar NIC controllers. The Pulse Shaper &
Filter employs a digital finite impulse response filter (FIR) to pre-
compensate for line distortion and to remove high frequency
components in accordance with the 802.3 Standard. The Pulse
Shaper & Filter is disabled when not in 10BASE-T mode.
125MHz Synthesizer
This synthesizer employs a phase-locked loop (PLL) to
generate a 125MHz timing reference from the 25MHz reference
clock. This 125MHz reference is used by the 100BASE-TX
transmit function and is divided by 5 to provide a 25MHz data
strobe on TXC. TXC is frequency and phase locked to the
25MHz reference with a small phase offset. The synthesizer is
disabled when not in 100BASE-TX mode.
TX10 Driver
The TX10 Driver operates with 1:1 magnetics to provide
impedancematchingandamplificationofthesignalinaccordance
with the 802.3 specifications. The transmit current is governed
bythecurrentthroughtheTXREF10pin,whichmustbegrounded
through a resistor as described in “External Components”.
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