Intel® 820E Chipset

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4.7.Unused Outputs

All unused clock outputs must be tied to ground through a series resistor that has approximately the impedance of the output buffer (shown in the following table). These resistors are designed to terminate unused outputs to eliminate EMI.

Table 60. Unused Output Termination

Buffer Name

VCC Range

Impedance

If Unused Output

 

(V)

()

Termination to Vss ()

 

 

 

 

CPU, CPU_Div2, IOAPIC

2.375 – 2.625

13.5 – 45

30

 

 

 

 

48 MHz, REF

3.135 – 3.465

20 – 60

40

 

 

 

 

PCI, 3V66

3.135 – 3.465

12 – 55

33

 

 

 

 

4.8.Decoupling Recommendation for CK133 and DRCG

Some CK133 vendors may integrate the XTAL_IN and XTAL_OUT frequency adjust capacitors. However, pads should be placed on the board for these external capacitors for testing/debug.

To further reduce jitter and voltage supply noise, it is advisable to add a ferrite filter with 2 caps (10 µF and 0.1 µF) on both the 2.5 V and 3.3 V planes, close to the clock devices. This applies to both DRCG and CK133.

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Design Guide

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Image 174
Intel 820E manual Unused Outputs, Decoupling Recommendation for CK133 and Drcg, Unused Output Termination