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Ethernet Physical Transceiver (EPHY)
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
19-29
Figure 19-22. 100BASE-TX Block Diagram
19.4.4.1
Sublayers
19.4.4.1.1
PCS Sublayer
The PCS sublayer is the MII interface that provides a uniform interface to the reconciliation sublayer.
The services provided by the PCS include:
•
Encoding/decoding of MII data nibbles to/from 5-bit code-groups (4B/5B)
•
Carrier sense and collision indications
•
Serialization/deserialization of code-groups for transmission/reception on the PMA
•
Mapping of transmit, receive, carrier sense, and collision detection between the MII and the
underlying PMA
Serial to Parallel and Symbol Alignment:
This block looks for the occurrence of the JK symbol to align
the serial bit stream and convert it to a parallel format.
Carrier Sense:
In full-duplex mode, carrier sense is only asserted while the receive channel is active
.
The
carrier sense examines the received data bit stream looking for the SSD, the JK symbol pair. In the idle
state, IDLE symbols (all logic ones) are received. If the first 5-bit symbols received after an idle stream
forms the J symbol (11000) it asserts the CRS signal. At this point the second symbol is checked to confirm
the K symbol (10001). If successful, the following aligned data (symbols) are presented to the 4B/5B
decoder. If the JK pair is not confirmed, the false carrier detect is asserted and the idle state is re-entered.
Carrier sense is de-asserted when the ESD (end-of-stream) delimiter, the TR symbol pair, is found, or when
an idle state is detected.
In half-duplex, CRS is also asserted on transmit.
Parallel to Serial:
This block takes parallel data and converts it to serial format.
TX
RX
MII
4B5B
Encoder
Decoder
4B5B
Serial to
Parallel
Parallel
to
Serial
Digital
Loopback
(bit 0.14)
Descrambler
Scrambler
Carrier
Sense
Decoder
MLT3
Encoder
MLT3
Slope
Control
Line
Driver
Link
Monitor
Analog
Loopback
(bit 18.4)
Equalizer
and
Timing
Recovery
Wander
Baseline
PCS
PMD
and Symbol
Alignment
PMA
PMA
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