Intel 815 - Manual (Page 34)

Universal Socket 370 Design
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34 Intel
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815 Chipset Platform Design Guide
4.2.4 VTT Processor Pin AG1
Processor pin AG1 requires additional attention since it is a ground pin on a Pentium III processor
(CPUID=068xh) / Celeron processor (CPUID=068xh) and a VTT pin on a future 0.13 micron
socket 370 processor. A separate switch controlled by the TUAL5 reference schematic signal
determines whether pin AG1 is pulled to ground or VTT. Refer to Figure 10 for an example
implementation.
Figure 10. Switching Pin AG1
1 K Ω
Processor Pin
AG1
TUAL5
VTT
Note: The FET m ust have no m ore than
100 m illiohm s resistance between the
source and the drain.
AG1_Switch
4.2.5 Identifying the Processor at the GMCH
The GMCH determines whether the socket contains a future 0.13 micron socket 370 processor or
Pentium III processor (CPUID=068xh) / Celeron processor (CPUID=068xh) based on the input to
pin SMAA12 on the GMCH. In a system using future 0.13 micron socket 370 processors,
SMAA12 will be pulled down during reset to indicate to the GMCH that a future 0.13 micron
socket 370 processor is in the socket. Refer to Figure 11. for an example implementation.