82801BA Datasheet, PDF (81/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Functional Description
5.2.5
CSMA/CD Unit
The ICH2 integrated LAN Controller CSMA/CD unit implements both the IEEE 802.3 Ethernet
10 Mbps and IEEE 802.3u Fast Ethernet 100 Mbps standards. It also supports the 1 Mbps Home
Phoneline Networking Alliance (HomePNA*) specification effort. It performs all the CSMA/CD
protocol functions such as transmission, reception, collision handling, etc. The LAN Controller
CSMA/CD unit interfaces to the 82562ET/EM 10/100 Mbps Ethernet or the 82562EH 1 Mbps
HomePNA*-compliant LAN Connect component through the ICH2’s LAN Connect interface
signals.
Full Duplex
When operating in full duplex mode, the LAN Controller can transmit and receive frames
simultaneously. Transmission starts regardless of the state of the internal receive path. Reception
starts when the LAN Connect component detects a valid frame on its receive differential pair.
When in Full Duplex mode, the ICH2 integrated LAN Controller also supports the IEEE 802.3x
flow control standard.
The LAN Controller operates in either half duplex mode or full duplex mode. For proper operation,
both the LAN Controller CSMA/CD module and the discrete LAN Connect component must be set
to the same duplex mode. The CSMA duplex mode is set by the LAN Controller Configure
command or forced by automatically tracking the mode in the LAN Connect component.
Following reset, the CSMA will default to automatically track the LAN Connect component
duplex mode.
The selection of duplex operation (full or half) and flow control is done in two levels: MAC and
LAN Connect.
Flow Control
The LAN Controller supports IEEE 802.3x frame based flow control frames only in full duplex
switched environments. The LAN Controller flow control feature is not intended to be used in
shared media environments.
Flow control is optional in full duplex mode and is selected through software configuration. There
are three modes of flow control that can be selected: frame-based transmit flow control, frame-
based receive flow control, and none.
Address Filtering Modifications
The LAN Controller can be configured to ignore one bit when checking for its Individual Address
(IA) on incoming receive frames. The address bit, known as the Upper/Lower (U/L) bit, is the
second least significant bit of the first byte of the IA. This bit may be used, in some cases, as a
priority indication bit. When configured to do so, the LAN Controller passes any frame that
matches all other 47 address bits of its IA, regardless of the U/L bit value.
This configuration only affects the LAN Controller specific IA and not multicast, multi-IA or
broadcast address filtering. The LAN Controller does not attribute any priority to frames with this
bit set, it simply passes them to memory regardless of this bit.
VLAN Support
The LAN Controller supports the IEEE 802.1 standard VLAN. All VLAN flows are implemented
by software. The LAN Controller supports the reception of long frames; specifically frames longer
than 1518 bytes, including the CRC, if software sets the Long Receive OK bit in the Configuration
command. Otherwise, “long” frames are discarded.
82801BA ICH2 and 82801BAM ICH2-M Datasheet
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