I/O Subsystem
R
226
Intel
®
855PM Chipset Platform Design Guide
Figure 126. RTC Power Well Isolation Control
BAV99
BAV99
2.2K
Ω
No Stuff
No Stuff
MMBT3906
10K
Ω
RSMRST#
ICH4-M
RSMRST#
generation
from MB logic
9.11.
CPU I/O Signals Considerations
The Intel 82801DBM ICH4-M has been designed to be voltage compatible with the CMOS signals of
the processor. For Intel Pentium M/Intel Celeron M processor-based systems, the ICH4-M’s V_CPU_IO
rail uses the same 1.05-V voltage as the V
CCP
rails for the processor and Intel 855PM chipset. It is
important to verify that the voltage requirements of all processor and ICH4-M signals are compatible
with the FWH as well. See Section 9.7 for FWH details. Figure 127 shows a typical interface between
the ICH4-M, CPU, and FWH. See Section 4.1.4 for recommended topologies and routing guidelines.