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Intel
855GME Chipset and Intel
amount of current is the limiting agent on how small the resistor may be. The pull-up resistor
may not be made so large that the bus time constant (Resistance X Capacitance) does not meet
the SMBus rise and time specification.
•
The maximum bus capacitance that a physical segment may reach is 400 pF.
•
The 6300ESB does not run SMBus cycles while in S3.
•
SMBus devices that may operate in STR must be powered by the V
•
When the SMBus is connected to the PCI Bus, it must be connected to all PCI slots in the
system.
9.8.1.3
High Power/Low Power Mixed Architecture
This design allows for current isolation of high and low current devices while also allowing
SMBus devices to communicate while in S3. V
non-essential devices on the core supply. This is accomplished by the use of a FET to isolate the
devices powered by the core and suspend supplies. See
Figure 117.
High Power/Low Power Mixed V
Non-Standby
Devices
V
V
CC
CC
SMBus
NOTES:
1. Added considerations for mixed architecture.
2. The bus switch must be powered by V
3. Devices powered by the V
accomplished with the bus switch.
4. The bus bridge can be a device like the Philips* PCA9515.
9.8.1.4
Calculating the Physical Segment Pull-Up Resistor
The following tables are provided as a reference for calculating the value of the pull-up resistor that
may be used for a physical bus segment. When any physical bus segment exceeds 400 pF, then a
bus bridge device such as the Philips Semiconductor* PCA9515 must be used to separate the
physical segment into two segments that individually have a bus capacitance less than 400 pF.
Devices running
in Standby
V
Sus3_3
V
CC
CC
Buffered Power
Good signal from
Power Supply
LOW CURRENT
_SUSPEND well must not drive into other devices that are powered off. This is
CC
January 2007
®
6300ESB ICH Embedded Platform Design Guide
Intel
_
leakage is minimized by keeping
CC
SUSPEND
Figure
_
/V
_
CC
SUSPEND
CC
CORE
Devices running
in Standby
Sus
V
Sus
CC
Bus
Bridge
SMBus
®
Intel
6300ESB
I/O Controller
Hub
_SUSPEND.
CC
®
6300ESB Design Guidelines
_
supply.
CC
SUSPEND
117.
Architecture
Non-Standby
Devices
V
Sus3_3
V
CC
CC
SMBus
Buffered Power
Good signal from
Power Supply
HIGH CURRENT
V
CC
B2898-01
223
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