Mobile Intel Pentium 4 Processor - M and Intel 845MP/MZ Chipset Platform Design Guide

Mobile Intel
®
Pentium
®
4 Processor-M and Intel
®
845MP/845MZ Chipset Platform
Design Guide 115
R
Figure 57. Mixed Vcc_Suspend/Vcc_Core Architecture
Vcore
ICH3
Vsus
Vsus Vsus
SMBus 2.0
BUS
SWITCH
OE#
SLP_S3#
Vsus
Vcore
SMBus2.0
Vsus
Devices running in Standby
Non-Standby devices
Vcore
Added Considerations for Mixed Architecture:
• The bus switch must be powered by Vcc_Suspend
• If there are 5-V SMBus devices used, then an added level translator must be used to separate those
devices driving 5 V from those driving 3-V signal levels.
• Devices that are powered by the Vcc_Suspend well must not drive into other devices that are
powered off. This is accomplished with the “bus switch”.
9.7. FWH
The following provides general guidelines for compatibility and design recommendations for supporting
the FWH device. The majority of the changes will be incorporated in the BIOS. Refer to the FWH BIOS
Specification or equivalent (contact your Field Representative for more information).
9.7.1. FWH Decoupling
A 0.1-µF capacitor should be placed between the Vcc supply pins and the Vss ground pins to decouple
high frequency noise, which may affect the programmability of the device. Additionally, a 4.7-µF
capacitor should be placed between the Vcc supply pins and the Vss ground pins to decouple low
frequency noise. The capacitors should be placed no further than 390 mils from the Vcc supply pins.
9.7.2. In Circuit FWH Programming
All cycles destined for the FWH will appear on PCI. The ICH3-M hub interface to PCI Bridge will put
all CPU boot cycles out on PCI (before sending them out on the FWH interface). If the ICH3-M is set for
subtractive decode, these boot cycles can be accepted by a positive decode agent on the PCI bus. This
enables the ability to boot from of a PCI card that positively decodes these memory cycles (In order to
boot off a PCI card it is necessary to keep the ICH3-M in subtractive decode mode). If a PCI boot card is
inserted and the ICH3-M is programmed for positive decode, there will be two devices positively
decoding the same cycle. In systems with the 82380AB (ISA bridge), it is also necessary to keep the
NOGO signal asserted when booting from a PCI ROM. Note that it is not possible to boot off a ROM
behind the 82380AB. Once booted from the PCI card, you could potentially program the FWH in circuit
and program the ICH3-M CMOS.