FSB Design Guidelines
R
Intel
®
855PM Chipset Platform Design Guide
75
4.1.10. Processor
V
CCSENSE
/V
SSSENSE
Design Recommendations
The VCCSENSE and VSSSENSE signals of the processor provide isolated, low impedance connections
to the processor’s core power (VCC) and ground (VSS). These pins can be used to sense or measure
power (VCC) or ground (VSS) near the silicon with little noise. To make them available for
measurement purposes, it is recommended that VCCSENSE and VSSSENSE both be routed with a Zo =
55
± 15% trace of equal length. Use 3:1 spacing between the routing for the two signals and all other
signals should be a minimum of 25 mils (preferably 50 mils) from VCCSENSE and VSSSENSE
routing. Terminate each line with an optional (default is No Stuff) 54.9
± 1% resistor. Also, a ground
via spaced 100 mils away from each of the test point vias for VCCSENSE and VSSSENSE should be
added. A third ground via should also be placed in between them to allow for a differential probe
ground. See Figure 40 for the recommended layout example.
Figure 40. V
CCSENSE
/V
SSSENSE
Routing Example
VCCSENSE
GND
54.9
Ω
54.9
Ω
VSSSENSE
100mil