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11.5.2. Mixing Processors of Different Frequencies
Mixing components of different internal clock frequencies is not supported and has not been val-
idated by Intel. One should also note when attempting to mix processors rated at different fre-
quencies in a multi-processor system that a common bus clock frequency and a set of multipliers
must be found that is acceptable to all processors in the system. Of course, a processor may be
run at a core frequency as low as its minimum rating. Operating system support for multi-
processing with mixed frequency components should also be considered.
Note that in order to support different frequency multipliers to each processor, the design shown
above would require four multiplexers.
11.6.
VOLTAGE IDENTIFICATION
There are 4 Voltage Identification Pins on the Pentium Pro processor package. These pins can
be used to support automatic selection of power supply voltages. These pins are not signals but
are each either an open circuit in the package or a short circuit to V ss . The opens and shorts de-
fines the voltage required by the processor. This has been added to cleanly support voltage spec-
ification variations on future Pentium Pro processors. These pins are named VID0 through VID3
and the definition of these pins is shown in Table 11-1. A '1' in this table refers to an open pin
and '0' refers to a short to ground. The V cc P power supply should supply the voltage that is
requested or disable itself.
Table 11-1. Voltage Identification Definition 1, 2
VID[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
NOTES:
1. Nominal setting requiring regulation to ±5% at the Pentium
port not expected for 2.1V-2.3V.
2. 1= Open circuit; 0= Short to V ss
Voltage setting
3.5
3.4
3.3
3.2
3.1
3.0
2.9
2.8
ELECTRICAL SPECIFICATIONS
VID[3:0]
Voltage Setting
1000
1001
1010
1011
1100
1101
1110
1111
No CPU Present
®
Pro processor pins under all conditions. Sup-
2.7
2.6
2.5
2.4
2.3
2.2
2.1
11-7
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