Resistive Compensation - Intel 855PM Design Manual

Platform Design Checklist
14.6.3.

Resistive Compensation

Pin Name
GRCOMP
HLRCOMP
HRCOMP[1:0]
SMRCOMP
300
MCH – Resistive Compensation
System
Pull up/Pull down
Pull down to GND 36.5
Pull up to Vcc1_8 36.5
Pull down to GND 27.4
Pull up to 30.1
Vcc1_25[DDR_Vtt]
± 1% GRCOMP resistor value = 2/3 * AGP routing channel
impedance.
Intel CRB uses 40.2
GRCOMP.
± 1% HLRCOMP resistor value = 2/3 * board impedance.
± 1% Each signal should be pulled down to ground through a
27.4 ± 1% resistor with a Zo = 27.4
Max trace length from pin to resistor should be < 0.5"
and ~18 mils wide. Recommend routing 25 mils away
from any switching signal.
See Section 4.1.8.2 for details.
± 1% In S3, Vcc1_25[DDR_Vtt] (DDR channel termination
voltage) can be turned OFF.
One 0.1 µF decoupling cap is required for this signal.
®
Intel 855PM Chipset Platform Design Guide
Notes
± 1% pull down resistor for
trace.
R