DM9000
ISA to Ethernet MAC controller with integrated 10/100 PHY
Final
35
Version: DM9000-DS-F01
April 12, 2002
9.6.8 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.
9.6.9 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.
9.7 10Base-T Operation
The 10Base-T transceiver is IEEE 802.3u compliant.
When the DM9000 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 the
Manchester encoded. When receiving, the bit stream,
encoded by the Manchester, is decoded and
converted into nibble format to present to the MII
interface.
9.8 Collision Detection
For half-duplex operation, a collision is detected when
the transm it and rec eive cha nnels ar e ac tive
simultaneously. When a collision is detected, it will be
reported by the COL signal on the MII interface.
Collision detection is disabled in F ull Duplex
operation.
9.9 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.
9.10 Auto-Negotiation
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.
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.
