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Figure 4-13. Single Hub Interface Reference Divider Circuit
Figure 4-14. Locally Generated Hub Interface Reference Dividers
G M C H
4.7.4
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 Intel
82801AA (ICH) and Intel
compensation. It can be used as either Impedance Compensation (ZCOMP) or Resistive
Compensation (RCOMP). The guidelines are below:
RCOMP: Tie the HLCOMP pin to a 40 Ω 1% or 2% pull-up resistor (to 1.8V) via a 10 mil
•
wide, 0.5" trace (targeted for a nominal trace impedance of 40 Ω).
•
ZCOMP: The HLCOMP pin should be tied to a 10 mil trace that is AT LEAST 18" long. This
trace should 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 GMCH 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.
®
Intel
810A3 Chipset Design Guide
300 Ω
G M C H
H U B R E F
0.01 uF
1.8V
300 Ω
H U B R E F
300 Ω
®
82801AB (ICH0) I/O Controller Hub Datasheet for details on
1.8V
0.01 uF
300 Ω
0.1 uF
0.01 uF
0.01 uF
Layout and Routing Guidelines
ICH
H U B R E F
1.8V
300 Ω
ICH
H U B R E F
300 Ω
®
4-11
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