78Q2123/78Q2133 MicroPHY™
10/100BASE-TX Transceiver
In 10BASE-T mode, the 20MHz receive clock is
recovered digitally from the Manchester data using a
PCS Bypass Mode (Auto-negotiate must be off)
The PCS Bypass mode is entered by setting register
bit MR 16.1. In this mode the 78Q2123/78Q2133
accept scrambled 5 bit code words at the TX_ER
and TXD[3:0] pins, TX_ER being the MSB of the
data input. The 5 bit code groups are converted to
MLT-3 signal for transmission.
The received MLT-3 signal is converted to 5 bit NRZ
code groups and output from the RX_ER and
RXD[3:0] pins, RX_ER being the MSB of the data
output. The RX_DV and TX_EN pins are unused in
PCS Bypass mode.
DLL locked to the reference clock.
When
Manchester-coded preambles are detected, the
CDR immediately re-aligns the phase of the clock to
synchronize with the incoming data. Hence clock
acquisition is fast and immediate.
100BASE-TX OPERATION
100BASE-TX Transmit
The 78Q2123/78Q2133 contain all of the necessary
circuitry to convert the transmit MII signaling from a
MAC to an IEEE-802.3 compliant data-stream
driving Cat-5 UTP cabling.
The internal PCS
10BASE-T OPERATION
10BASE-T Transmit
interface maps 4 bit nibbles from the MII to 5 bit
code groups as defined in Table 24-1 of IEEE-802.3.
These 5 bit code groups are then scrambled and
converted to a serial stream before being sent to the
MLT-3 pulse shaping circuitry and line driver. The
pulse-shaper uses current modulation to produce
the desired output waveform. Controlled rise/fall
time in the MLT-3 signal is achieved using an
accurately controlled voltage ramp generator. The
line driver requires an external 1:1 isolation
transformer to interface with the line media. The
center-tap of the primary side of the transformer
must be connected to the Vcc supply (3.3V ± 0.3V).
The 78Q2123/78Q2133 take 4-bit parallel NRZ data
via the MII interface and passes it through a parallel
to serial converter. The data is then passed through
a Manchester encoder, pre-emphasis pulse-shaper,
media filter, and finally to the twisted-pair line driver.
The pulse-shaper and filter ensure the output
waveforms meet the voltage template and spectral
content requirements detailed in Clause 14 of IEEE-
802.3. Interface to the twisted-pair media is through
a center-tapped 1:1 transformer.
No external
filtering is required. During auto-negotiation and
10BASE-T idle periods, link pulses are transmitted.
100BASE-TX Receive
The 78Q2123/78Q2133 employ an onboard timer to
prevent the MAC from capturing a network through
excessively long transmissions. When this timer
expires, the chip enters the jabber state and
transmission is halted. The jabber state is exited
after the MII goes idle for 500±250ms.
The 78Q2123/78Q2133 receive a 125MBaud MLT-3
signal through a 1:1 transformer. The signal then
goes through a combination of adaptive offset
adjustment (baseline wander correction) and
adaptive equalization. The effect of these circuits is
to sense the amount of dispersion and attenuation
caused by the cable and transformer, and restore
the received pulses to logic levels. The amount of
gain and equalization applied to the pulses varies
with the detected attenuation and dispersion and,
10BASE-T Receive
The 78Q2123/78Q2133 receive Manchester-
encoded 10BASE-T data through the twisted pair
inputs and re-establishes logic levels through a
slicer with a smart squelch function. The slicer
automatically adjusts its level after detection of valid
data with the appropriate levels. Data is passed on
to the CDR where the clock is recovered, and the
data is re-timed and decoded. From there, data
therefore, with the length of the cable.
The
78Q2123/78Q2133 can compensate for cable loss
of up to 10dB at 16 MHz. This loss is represented
as test_chan_5 in Annex
A
of the ANSI
X3.263:199X. The equalized MLT-3 data signal is
bi-directionally sliced and the resulting NRZI bit-
stream is presented to the CDR where it is re-timed
and decoded to NRZ format. The re-timed serial
data passes through a serial-to-parallel converter,
then descrambled and aligned into 5 bit code
groups. The receive PCS interface maps these
code groups to 4 bit data for the MII as outlined in
Table 24-1 in Clause 24 of IEEE-802.3.
enters
the
serial-to-parallel
converter
for
transmission to the MAC via the Media Independent
Interface. Interface to the twisted-pair media is
through an external 1:1 transformer.
Polarity
information is detected and corrected within internal
circuitry.
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© 2009 Teridian Semiconductor Corporation
Rev 1.5
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