DM9016
3-port switch with Processor Interface
9.4.2.8 Code Group Alignment
9.4.5 Carrier Sense
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.
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.
9.4.2.9 4B5B Decoder
9.4.6 Auto-Negotiation
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 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.
The T/R symbol pair is also stripped from the nibble,
presented to the Reconciliation layer.
9.4.3 10Base-T Operation
The 10Base-T transceiver is IEEE 802.3u compliant.
When the DM9016 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.
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.
9.4.4 Collision Detection
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.
Preliminarydatasheet
DM9016-13-DS-P01
March 26, 2009
77
DAVICOM [ DAVICOM SEMICONDUCTOR, INC. ]
