82870P2P64H2 Datasheet, PDF (200/217 Pages) –

Electrical Characteristics
R
5.2.2.4
Spread Spectrum Clocking
Spread spectrum clocking can be used on the P64H2 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:
f

=


(1 − δ ) f _nom
+ 2 f_m
⋅δ
⋅
f _nom
⋅t
_{(1 + δ )}

f _nom
−
2
f_m
⋅δ
⋅
f _nom
⋅t
when 0 < t < ¹ ;
2 f_m
when ¹ < t < ¹ ,
2 f_m
f_m
where:
f_nom is the nominal frequency in the non-SSC mode
f_m is the modulation frequency
f_m is the modulation amount
t is time.
200
Intel^® 82870P2 P64H2 Datasheet