Ethernet Physical Transceiver (EPHY)
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
19-31
restoration to restore the lost DC component of the recovered digital data to correct the baseline wander
problem.
Timing Recovery
: The timing recovery block locks onto the incoming data stream, extracts the embedded
clock, and presents the data synchronized to the recovered clock.
In the event that the receive path is unable to converge to the receive signal, it resets the MSE-good (bit
25.15) signal. The clock synthesizer provides a center frequency reference for operation of the clock
recovery circuit in the absence of data.
Adaptive Equalizer:
At a data rate of 125 Mbps, the cable introduces significant distortion due to high
frequency roll off and phase shift. The high frequency loss is mainly due to skin effect, which causes the
conductor resistance to rise as the square of the frequency.
The adaptive equalizer compensates for signal amplitude and phase distortion incurred from transmitting
with different cable lengths.
Loopback
: If asserted by bit 0.14, data encoded by the MLT3 encoder block is looped back to the MLT3
decoder block while the transmit and receive paths are disconnected from the media.
A second loopback mode for 100BASE-TX is available by setting bit 18.13 (MII loopback) to a logical 1.
This loopback mode takes the MII transmit data and loops it directly back to the MII receive pins. Again,
the transmit and receive paths are disconnected from the media.
MII loopback has precedence over the digital loopback if both are enabled at the same time.
A third loopback mode is available by setting bit 18.4 high. This analog loopback mode takes the MLT3
encoded data and loops it back through the base line wander and analog receive circuits.
Line Transmitter and Line Receiver:
These analog blocks allow EPHY to drive and receive data to/from
the 100BASE-TX media. The transmitter is designed to drive a 100-
Ω
UTP cable.
Link Monitor
: The link monitor process is responsible for determining whether the underlying receive
channel is providing reliable data. If a failure is found, normal operation is disabled. As specified in the
IEEE 802.3 standard, the link is operating reliably if a signal is detected for a period of 330
μ
s.
Far End Fault
: While the auto-negotiation function is disabled, this function is used to exchange fault
information between the PHY and the link partner.
19.4.5
Low Power Modes
There are several reduced power configurations available for the EPHY.
19.4.5.1
Stop Mode
If the MCU executes a STOP instruction, the EPHY is powered down and all internal MII registers reset
to their default state. Upon exiting stop mode, the EPHY exits the power-down state and latch the values
previously written to the EPHYCTL0 and EPHYCTL1 registers. The MII registers have to be re-initialized
after the start-up delay (t
Start-up
) has expired.
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60