Design Guide
39
Platform Clock Routing Guidelines
NOTES:
1. The skew budget includes clock driver output pair to output pair jitter (differential jitter) and skew, clock skew
due to interconnect process variation, and static skew due to layout differences between clocks to all bus
agents.
2. This number does not include clock driver common mode (cycle to cycle) jitter or spread spectrum clocking.
3. The interconnect portion of the total budget for this specification assumes clock pairs are routed on multiple
routing layers and routed no longer than the maximum recommended lengths.
Table 4-3. HOST_CLK[1:0]# Routing Guidelines
Layout Guideline
Value
Illustration
Notes
HOST_CLK Skew between Agents
300 ps total budget:
150 ps for clock driver
150 ps for interconnect
and
1,2,3,4
Trace Width
5 mils
Differential Pair Spacing
20 – 25 mils
5,6
Spacing to Other Traces
25 mils
Serpentine Spacing
Maintain a minimum S/h ratio
of > 5/26
Keep parallel serpentine
sections as short as possible.
Minimize 90 degree bends.
Make 45 degree bends, if
possible.
Motherboard Impedance – Differential
100
Ω
typical
8
Motherboard Impedance – Single Ended
50
Ω
± 10%
9
Processor Routing Length –
L1, L1’: Clock Driver to Rs
0 – 0.5”
13
Processor Routing Length –
L2, L2’: Rs to Rs-Rt Node
0 – 0.2”
13
Processor Routing Length –
L3, L3’: Rs-Rt Node to Rt
0 – 0.2”
13
Processor Routing Length –
L4, L4’: Rs-Rt Node to Load
0 – 22”
MCH Routing Length –
L1, L1’: Clock Driver to Rs
0 – 0.5”
13
MCH Routing Length –
L2, L2’: Rs to Rs-Rt Node
0 – 0.2”
13
MCH Routing Length –
L3, L3’: Rs-Rt Node to Rt
0 – 0.2”
13
MCH Routing Length –
L4, L4’: Rs-Rt Node to Load
0 – 22”
Processor to MCH Length Matching (LT)
0.035” ± 0.010”
MCH LT must be 0.076”
longer than Processor LT.
10
Processor to Processor Length Matching (LT)
±
10 mils
15
HOST_CLK0 – HOST_CLK1 Length Matching
± 10 mils
Rs Series Termination Value
20 – 33
Ω
±
5%
11
Rt Shunt Termination Value
49.9
Ω
±
1%
(for 50
Ω
board impedance)
12
Summary of Contents for Xeon
Page 24: ...Introduction 24 Design Guide This page is intentionally left blank ...
Page 30: ...Component Quadrant Layout 30 Design Guide This page is intentionally left blank ...
Page 52: ...Platform Clock Routing Guidelines 52 Design Guide This page is intentionally left blank ...
Page 66: ...System Bus Routing Guidelines 66 Design Guide This page is intentionally left blank ...
Page 118: ...Intel 82870P2 P64H2 118 Design Guide This page is intentionally left blank ...
Page 146: ...I O Controller Hub 146 Design Guide This page is intentionally left blank ...
Page 148: ...Debug Port 148 Design Guide This page is intentionally left blank ...
Page 210: ...Schematic Checklist 210 Design Guide This page is intentionally left blank ...
Page 220: ...Layout Checklist 220 Design Guide This page is intentionally left blank ...
Page 222: ...Schematics 222 Design Guide This page is intentionally left blank ...