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Figure 6. Power Pins of the Pentium
ò
Pro Processor Package - Top View (Through the Package)
A system designer planning for upgrade potential should
also be aware that future devices beyond the Pentium Pro
processor may require a voltage other than 3.1V. This
may range from 2.5V to 3.5V. To support this level of
upgrade potential, the power source for the
main
processor supply should be designed with the ability to
be easily configured to provide a voltage within the
range of 2.4V to 3.5V. Note that the cache will either run
at the
same voltage
as the processor,
or
at 3.3V, using
the cache support pins. One easy way to support this
range is with a replaceable power module. Another is by
changing the set point of the regulator via a variable
resistor, or by using the processor’s Voltage ID pins with
a resistor tree or a Digital to Analog converter (DAC).
The voltage ID scheme is described fully in the
Pentium
a
Pro Processor Developer’s Manual, Volume 1
. Intel has
worked with power supply vendors to create replaceable
voltage regulators which support voltage selection. See
your local field applications engineer for assistance.
Another voltage is required for the GTL+ bus. This level
is called V
TT
, and is set at 1.5V. This voltage is discussed
in Section 5, but is important in the discussion of Voltage
Sequencing in Section 3.3 as well.
3.3.
Voltage Sequencing
When designing a system with multiple voltages, there is
always the issue of ensuring that no damage occurs to the
system during
voltage sequencing.
Voltage sequencing is
the timing relationship between two or more voltages,
such as 3.3V and V
CC
P. Sequencing applies when the
power supply is turned on or off, or enters a failure