Electrical Characteristics
4.3.3.1
Spread Spectrum Clocking
Spread spectrum clocking can be used on the Intel® 6702PXH 64-bit PCI Hub to reduce energy.
Spread Spectrum clocking is a common technique used by system designers to meet FCC
emissions, where the frequency is deliberately shifted around to spread the energy off of the peak.
The following is to be observed when using Spread Spectrum clocking:
1. All device timings (including jitter, skew, min/max clock period, output rise/fall time) MUST
meet the existing non-spread spectrum specifications
2. All non-spread Host and PCI functionality must be maintained in the spread spectrum mode
(includes all power management functions).
3. The minimum clock period cannot be violated. The preferred method is to adjust the spread
technique to not allow for modulation above the nominal frequency. This technique is often
called “down-spreading”. The modulation profile in a modulation period can be expressed as:
Equation 4-1. Modulation Profile in a Modulation Period
1
0 < t < -------
2fm
(1 – δ )fnom + 2fm ⋅ δ ⋅ fnom ⋅ t
when
when
f
=
{
1
1
(1 + δ )fnom – 2fm ⋅ δ ⋅ fnom ⋅ t
------- < t < ----
2fm
fm
where:
f
nom is the nominal frequency in the non-SSC mode
fm is the modulation frequency
fm is the modulation amount
t is time
§
176
Intel® 6702PXH 64-bit PCI Hub Datasheet
INTEL [ INTEL ]
