DM8203
2-port switch with MII / RMII Interface
9.4.2.8 Code Group Alignment
9.4.6 Auto-Negotiation
The Code Group Alignment block receives un-aligned
5B data from the descrambler and converts it into 5B
code group data. Code Group Alignment occurs after
the J/K is detected and subsequent data is aligned on
a fixed boundary.
The objective of Auto-negotiation is to provide a
means to exchange information between linked
devices and to automatically configure both devices
to take maximum advantage of their abilities. It is
important to note that Auto-negotiation does not test
the characteristics of the linked segment. The
Auto-Negotiation function provides a means for a
device to advertise supported modes of operation to
a remote link partner, acknowledge the receipt and
understanding of common modes of operation, and to
reject un-shared modes of operation. This allows
devices on both ends of a segment to establish a link
at the best common mode of operation. If more than
one common mode exists between the two devices, a
mechanism is provided to allow the devices to
resolve to a single mode of operation using a
predetermined priority resolution function.
9.4.2.9 4B5B Decoder
The 4B5B Decoder functions as a look-up table that
translates incoming 5B code groups into 4B (Nibble)
data. When receiving a frame, the first 2 5-bit code
groups receive the start-of-frame delimiter (J/K
symbols). The J/K symbol pair is stripped and two
nibbles of preamble pattern are substituted. The last
two code groups are the end-of-frame delimiter (T/R
Symbols).
The T/R symbol pair is also stripped from the nibble,
presented to the Reconciliation layer.
Auto-negotiation also provides a parallel detection
function for devices that do not support the
Auto-negotiation feature. During Parallel detection
there is no exchange of information of configuration.
Instead, the receive signal is examined. If it is
discovered that the signal matches a technology,
which the receiving device supports, a connection will
be automatically established using that technology.
This allows devices not to support Auto-negotiation
but support a common mode of operation to establish
a link.
9.4.3 10Base-T Operation
The 10Base-T transceiver is IEEE 802.3u compliant.
When the DM8203 is operating in 10Base-T mode,
the coding scheme is Manchester. Data processed
for transmit is presented in nibble format, converted
to a serial bit stream, then the Manchester encoded.
When receiving, the bit stream, encoded by the
Manchester, is decoded and converted into nibble
format.
9.5 HP Auto-MDIX Functional Descriptions
9.4.4 Collision Detection
The DM8203 supports the automatic detect cable
connection type, MDI/MDIX (straight through/cross
over). A manual configuration by register bit for MDI
or MDIX is still accepted.
For half-duplex operation, a collision is detected
when the transmit and receive channels are active
simultaneously. Collision detection is disabled in full
duplex operation.
When set to automatic, the polarity of MDI/MDIX
controlled timing is generated by 16-bits LFSR. The
switching cycle time is located from 200ms to 420ms.
The polarity control is always switch until detect
received signal. After selected MDI or MDIX,
This feature is able to detect the required cable
connection type. (Straight through or crossed over)
and make correction automatically
9.4.5 Carrier Sense
Carrier Sense (CRS) is asserted in half-duplex
operation during transmission or reception of data.
During full-duplex mode, CRS is asserted only during
Receive operations.
Preliminarydatasheet
DM8203-15-DS-P05
October 23, 2008
53
DAVICOM [ DAVICOM SEMICONDUCTOR, INC. ]
