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Intel
®
820E Chipset
R
Design Guide 95
Figure 57. SMBUS/SMLink Interface
82801BA
ICH2
Host controller
slave interface
SMBus
SMBCLK
SPD data
Temperature on
thermal sensor
Network
interface
card on PCI
Microcontroller
Intel
®
8255
Motherboard
LAN controller
Wire OR
(optional)
SMLink0
SMLink1
SMLink
SMBDATA
smbus_smlink_IF
Note: Intel does not support external access to the ICH2’s integrated LAN controller via the SMLink interface.
Also, Intel does not support access to the ICH2’s SMBus slave interface by the ICH2’s SMBUS host
controller.
The following table describes the pull-up requirements for different implementations of the SMBus and
SMLink signals.
Table 20. Pull-Up Requirements for SMBus and SMLink Signals
SMBus / SMLink Use Implementation
Alert-on-LAN* signals 4.7 kΩ pull-up resistors to 3.3 V
SB
are required.
GPIOs Pull-up resistors to 3.3 V
SB
and the signals must be allowed.
To change states on power-up. (For example, during power-up the ICH2
will drive heartbeat messages until the BIOS programs these signals as
GPIOs.) The values of the pull-up resistors depend on the loading on the
GPIO signal.
Unused 4.7 kΩ pull-up resistors to 3.3 V
SB
are required.