Intel VC820 Design Guide - Page 71
Compensation, Locally generated Hub Interface Reference Dividers
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Layout/Routing Guidelines Figure 2-35. Locally generated Hub Interface Reference Dividers 1.8V 1.8V 2.8.4 300Ω 300Ω HUBREF MCH 300Ω HubRef2.vsd 0.1uF 300Ω HUBREF ICH 0.1uF Compensation There are two options for the ICH hub interface compensation (HLCOMP). HLCOMP is used by the ICH to adjust buffer characteristics to specific board characteristics. Refer to the ICH Datasheet for details on compensation. It can be used as either Impedance Compensation (ZCOMP) or Resistive Compensation (RCOMP). The guidelines are below: • RCOMP: Tie the COMP pin to a 40 Ω 2% (or 39 Ω 1%) pull-up resistor (to 1.8V) via a 10 mil wide, very short (
Intel
®
820 Chipset
Design Guide
2-45
Layout/Routing Guidelines
2.8.4
Compensation
There are two options for the ICH hub interface compensation (HLCOMP). HLCOMP is used by
the ICH to adjust buffer characteristics to specific board characteristics. Refer to the ICH Datasheet
for details on compensation. It can be used as either Impedance Compensation (ZCOMP) or
Resistive Compensation (RCOMP). The guidelines are below:
•
RCOMP:
Tie the COMP pin to a 40
Ω
2% (or 39
Ω
1%) pull-up resistor (to 1.8V) via a 10 mil
wide, very short (<0.5”) trace.
•
ZCOMP:
The COMP pin must be tied to a 10 mil trace that is AT LEAST 18” long. This trace
must be unterminated and care should be taken when routing the signal to avoid crosstalk
(15–20 mil separation between this signal and any adjacent signals is recommended). This
signal may not cross power plane splits.
The MCH also has a hub interface compensation pin. This signal (HLCOMP) can be routed using
either the RCOMP method or ZCOMP method described for the ICH.
Figure 2-35. Locally generated Hub Interface Reference Dividers
HUBREF
HUBREF
1.8V
MCH
ICH
1.8V
300
Ω
300
Ω
300
Ω
300
Ω
0.1uF
0.1uF
HubRef2.vsd