Functional Description
5-8
Intel
82801BA ICH2 Datasheet
Serial CSMA/CD Unit Overview
The CSMA/CD unit of the ICH2 LAN Controller allows it to be connected to the 82562ET/EM
10/100 Mbps Ethernet LAN Connect components or the 82562EH 1 Mbps HomePNA*-compliant
LAN Connect component. The CSMA/CD unit performs all of the functions of the 802.3 protocol
such as frame formatting, frame stripping, collision handling, deferral to link traffic, etc. The
CSMA/CD unit can also be placed in a full duplex mode which allows simultaneous transmission
and reception of frames.
5.2.2
LAN Controller PCI Bus Interface
As a Fast Ethernet Controller, the role of the ICH2 integrated LAN Controller is to access
transmitted data or deposit received data. The LAN Controller, as a bus master device, initiates
memory cycles via the PCI bus to fetch or deposit the required data.
To perform these actions, the LAN Controller is controlled and examined by the processor via its
control and status structures and registers. Some of these control and status structures reside in the
LAN Controller and some reside in system memory. For access to the LAN Controller’s Control/
Status Registers (CSR), the LAN Controller acts as a slave (in other words, a target device). The
LAN Controller serves as a slave also while the processor accesses the EEPROM.
5.2.2.1
Bus Slave Operation
The ICH2 integrated LAN Controller serves as a target device in one of the following cases:
Processor accesses to the LAN Controller System Control Block (SCB) Control/Status
Registers (CSR)
Processor accesses to the EEPROM through its CSR
Processor accesses to the LAN Controller PORT address via the CSR
Processor accesses to the MDI control register in the CSR
PCI Configuration cycles
The size of the CSR memory space is 4 KB in the memory space and 64 bytes in the I/O space. The
LAN Controller treats accesses to these memory spaces differently.
Control/Status Register (CSR) Accesses
The integrated LAN Controller supports zero wait state single cycle memory or I/O mapped
accesses to its CSR space. Separate BARs request 4 KB of memory space and 64 bytes of I/O
space to accomplish this. Based on its needs, the software driver uses either memory or I/O
mapping to access these registers. The LAN Controller provides 4 KB of CSR space, which
includes the following elements:
System Control Block (SCB) registers
PORT register
EEPROM control register
MDI control register
Flow control registers
In the case of accessing the Control/Status Registers, the processor is the initiator and the LAN
Controller is the target.
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