Design Guide
127
I/O Controller Hub
Both the SMBus Host Controller and the SMBus Slave Interface obey the SMBus 1.1 protocol, so
the two interfaces can be externally wire-OR'd together to allow an external management ASIC
(such as 82550) to access targets on the SMBus as well as the ICH3-S Slave interface.
Additionally, the ICH3-S supports slave functionality, including the Host Notify protocol, on the
SMLink pins. This is done by connecting SMLink0 to SMBCLK and SMLink1 to SMBDATA.
Intel does not support external access of the ICH3-S's Integrated LAN Controller via the SMLink
interface. In addition, Intel does not support access of the ICH3-S's SMBus Slave Interface by the
ICH3-S's SMBus Host Controller. Refer to the
Intel
®
82801CA I/O Controller Hub 3 (ICH3-S)
Datasheet
for full functionality descriptions of the SMLink and SMBus interface.
9.5.1
SMBus Design Considerations
Designing an SMBus using the ICH3-S is based on the power supply source for the SMBus
microcontrollers. For the platform, all devices are powered by VCC_3.3; therefore, the preferred
design choice is the unified VCC_3.3 architecture.
9.5.2
General Design Note
The pull-up resistor size for the SMBus data and clock signals is dependent on the number of
devices present on the bus. A typical value is 8.2 k
Ω
± 5%
. This should prevent the SMBus signals
from floating, which could cause leakage in the ICH3-S and other devices.
9.5.3
The Unified VCC_CORE Architecture
In the unified VCC_CORE architecture, all SMBus devices are powered by the VCC_3.3 supply.
This architecture in
allows none of the devices to operate in STR, minimizing the load
on 3.3 V SUSPEND.
Figure 9-7. Intel
®
ICH3-S SMBus / SMLink Interface
Intel
®
ICH3-S
Host Controller and
Slave Interface
SMBus
SMBCLK
SPD Data
Temperature on
Thermal Sensor
Network
Interface Card
on PCI
Microcontroller
Motherboard
LAN
Controller
Wire OR
(optional)
SMLink0
SMLink1
SMLink
SMBDATA
Summary of Contents for Xeon
Page 24: ...Introduction 24 Design Guide This page is intentionally left blank ...
Page 30: ...Component Quadrant Layout 30 Design Guide This page is intentionally left blank ...
Page 52: ...Platform Clock Routing Guidelines 52 Design Guide This page is intentionally left blank ...
Page 66: ...System Bus Routing Guidelines 66 Design Guide This page is intentionally left blank ...
Page 118: ...Intel 82870P2 P64H2 118 Design Guide This page is intentionally left blank ...
Page 146: ...I O Controller Hub 146 Design Guide This page is intentionally left blank ...
Page 148: ...Debug Port 148 Design Guide This page is intentionally left blank ...
Page 210: ...Schematic Checklist 210 Design Guide This page is intentionally left blank ...
Page 220: ...Layout Checklist 220 Design Guide This page is intentionally left blank ...
Page 222: ...Schematics 222 Design Guide This page is intentionally left blank ...