Functional Description
5-18
Intel
82801BA ICH2 Datasheet
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, “l(fā)ong” frames are discarded.
5.2.5
Media Management Interface
The management interface allows the processor to control the LAN Connect component via a
control register in the ICH2 integrated LAN Controller. This allows the software driver to place the
LAN Connect in specific modes such as full duplex, loopback, power down, etc., without the need
for specific hardware pins to select the desired mode. This structure allows the LAN Controller to
query the LAN Connect component for status of the link. This register is the MDI Control Register
and resides at offset 10h in the LAN Controller CSR. The MDI registers reside within the LAN
Connect component, and are described in detail in the LAN Connect component’s datasheet. The
processor writes commands to this register and the LAN Controller reads or writes the control/
status parameters to the LAN Connect component through the MDI register.
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