DM9601
USB to Ethernet MAC Controller with Integrated 10/100 PHY
Preliminary
41
Version: DM9601-DS-P01
June 22, 2001
12.2.8 Code Group Alignment
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.
12.2.9 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 two 5-bit code
groups received are 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.
12.3 10Base-T Operation
The 10Base-T transceiver is IEEE 802.3u compliant.
When the DM9601 is operating in 10Base-T mode,
the coding scheme is Manchester. Data processed for
transmit is presented to the MII interface in nibble
format, converted to a serial bit stream, then
Manchester encoded. When receiving, the
Manchester encoded bit stream is decoded and
converted into nibble format for presentation to the MII
interface.
12.4 Collision Detection
For half-duplex operation, a collision is detected when
the transmit and receive channels are active
simultaneously. When a collision has been detected, it
will be reported by the COL signal on the MII interface.
Collision detection is disabled in Full Duplex
operation.
12.5 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.
12.6 Auto-Negotiation
The objective of Auto-negotiation is to provide a
means to exchange information between segment
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 link segment characteristics. 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.
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 configuration information, instead, the
receive signal is examined. If it is discovered that the
signal matches a technology that the receiving device
supports, a connection will be automatically
established using that technology. This allows devices,
which do not support Auto-negotiation but support a
common mode of operation, to establish a link.
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