Intel 815 - Manual (Page 37)

Universal Socket 370 Design
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Intel
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815 Chipset Platform Design Guide 37
4.2.7 VCMOS Reference
In previous platforms supporting the Pentium III processor (CPUID=068xh) and Celeron processor
(CPUID=068xh), VCMOS was generated by the processor itself. The future 0.13 micron socket
370 processors do not generate VCMOS, and the universal platform is required to generate this
separately on the motherboard. Processor pin AK22, which is a GTL_REF pin on a Pentium III
processor (CPUID=068xh) and Celeron processor (CPUID=068xh), has been changed to a
VCMOS_REF pin on future 0.13 micron socket 370 processors. Referring to Figure 13, a network
of resistors and a capacitor must be added so that this pin operates appropriately for whichever
processor is in the socket.
Figure 13. GTL_REF/VCMOS_REF Voltage Divider Network
75 Ω
1%
150 Ω
1%
VCMOS
Processor Pin
AK22
0.1 µ F
GTL_CMOS_Ref