Datasheet

 2017 Microchip Technology Inc. DS00002436B-page 19
KSZ8041TL/FTL/MLL
3.0 FUNCTIONAL DESCRIPTION
The KSZ8041TL is a single 3.3V supply Fast Ethernet transceiver. It is fully compliant with the IEEE 802.3u specifica-
tion.
On the media side, the KSZ8041TL supports 10BASE-T and 100BASE-TX with HP auto MDI/MDI-X for reliable detec-
tion of and correction for straight-through and crossover cables.
The KSZ8041TL offers a choice of MII, RMII, or SMII data interface connection to a MAC processor. The MII manage-
ment bus option gives the MAC processor complete access to the KSZ8041TL control and status registers. Additionally,
an interrupt pin eliminates the need for the processor to poll for PHY status change.
Physical signal transmission and reception are enhanced through the use of patented analog circuitries that make the
design more efficient and allow for lower power consumption and smaller chip die size.
The KSZ8041FTL has all the identical rich features of the KSZ8041TL plus 100BASE-FX fiber support.
The KSZ8041MLL is the basic 10BASE-T/100BASE-TX copper version with MII support.
3.1 100BASE-TX Transmit
The 100BASE-TX transmit function performs parallel-to-serial conversion, 4B/5B coding, scrambling, NRZ-to-NRZI con-
version, and MLT3 encoding and transmission.
The circuitry starts with a parallel-to-serial conversion, which converts the MII data from the MAC into a 125 MHz serial
bit stream. The data and control stream is then converted into 4B/5B coding, followed by a scrambler. The serialized
data is further converted from NRZ-to-NRZI format, and then transmitted in MLT3 current output.
The output current is set by an external 6.49 k 1% resistor for the 1:1 transformer ratio. It has typical rise/fall times of
4 ns and complies with the ANSI TP-PMD standard regarding amplitude balance, overshoot and timing jitter. The wave-
shaped 10BASE-T output drivers are also incorporated into the 100BASE-TX drivers.
3.2 100BASE-TX Receive
The 100BASE-TX receiver function performs adaptive equalization, DC restoration, MLT3-to-NRZI conversion, data and
clock recovery, NRZI-to-NRZ conversion, de-scrambling, 4B/5B decoding, and serial-to-parallel conversion.
The receiving side starts with the equalization filter to compensate for inter-symbol interference (ISI) over the twisted
pair cable. Since the amplitude loss and phase distortion is a function of the cable length, the equalizer must adjust its
characteristics to optimize performance. In this design, the variable equalizer makes an initial estimation based upon
comparisons of incoming signal strength against some known cable characteristics, and then tunes itself for optimiza-
tion. This is an ongoing process and self-adjusts against environmental changes such as temperature variations.
Next, the equalized signal goes through a DC restoration and data conversion block. The DC restoration circuit is used
to compensate for the effect of baseline wander and to improve the dynamic range. The differential data conversion
circuit converts the MLT3 format back to NRZI. The slicing threshold is also adaptive.
The clock recovery circuit extracts the 125 MHz clock from the edges of the NRZI signal. This recovered clock is then
used to convert the NRZI signal into the NRZ format. This signal is sent through the de-scrambler followed by the 4B/
5B decoder. Finally, the NRZ serial data is converted to the MII format and provided as the input data to the MAC.
3.3 PLL Clock Synthesizer
The KSZ8041TL/FTL/MLL generates 125 MHz, 25 MHz, and 20 MHz clocks for system timing. In MII mode, internal
clocks are generated from an external 25 MHz crystal or oscillator. For the KSZ8041TL/FTL, in RMII and SMII modes,
these internal clocks are generated from external 50 MHz and 125 MHz oscillators or system clocks, respectively.
3.4 Scrambler/De-scrambler (100BASE-TX Only)
The purpose of the scrambler is to spread the power spectrum of the signal in order to reduce EMI and baseline wander.
3.5 10BASE-T Transmit
The 10BASE-T drivers are incorporated with the 100BASE-TX drivers to allow for transmission using the same mag-
netic. The drivers also perform internal wave-shaping and pre-emphasize, and output 10BASE-T signals with a typical
amplitude of 2.5V peak. The 10BASE-T signals have harmonic contents that are at least 27 dB below the fundamental
frequency when driven by an all-ones Manchester-encoded signal.