DM9621 datasheet(53/66 Pages) DAVICOM

53 / 66 page

DM9621

USB2.0 to Fast Ethernet Controller

Preliminary

Version: DM9621 -14-DS-P02

February 23, 2011

7.2.18 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.

7.2.19 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 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.

7.2.20 10Base-T Operation

The 10Base-T transceiver is IEEE 802.3u compliant.

When the DM9621 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.

7.2.21 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.

7.2.22 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.

7.2.23 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.

7.2.24 Auto-Negotiation (continued)

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 that do not support Auto-negotiation

but support a common mode of operation to establish

a link.

DM9621 Datasheet(PDF) 53 Page - Davicom Semiconductor, Inc.

DM9621 Datasheet(HTML) 53 Page - Davicom Semiconductor, Inc.

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