Design Guide
73
Memory Interface Routing Guidelines
6.3
Command Clock Routing
Only one differential clock pair is routed to each DIMM connector because the MCH only supports
registered DDR DIMMs. All CMDCLK/CMDCLK# termination is on the DIMM modules. Route
each clock and its compliment adjacent to each other. The two complimentary signals (e.g.,
CMDCLK0 and CMDCLK0#) must be length matched to each other within ± 2 mils. Excluding
breakout, the maximum recommended layer changes is one. Ensure that the reference plane does
not change when switching layer.
NOTES:
1.
CMDCLK/CMDCLK# must be matched to within ± 2 mils using package trace length
compensation
.
2. The total trace length difference of any two CMDCLK/CMDCLK# pairs cannot exceed 4 inches for timing
reasons.
3. For 3-DIMM solutions, treat the CMDCLK3/CMDCLK3# pair as a no connect.
4. Indicated lengths measure from the MCH pin to the DIMM connector pin.
Table 6-4. Command Clock Pair Routing Guidelines
Parameter
Intel
®
E7500
Reference
Signal Group
CMDCLK[3:0], CMDCLK[3:0]#
Topology
Point to point
Reference Plane
Ground
Differential Trace Impedance (Zo)
100
Ω
± 10%
Nominal Trace Width
5 mil
Trace Spacing to Complement
5 mil
Trace Spacing to Other Traces
20 mil
Trace Length – MCH to DIMM1
2.1” to 10.0”
Trace Length – MCH to DIMM2
2.1” to 10.0”
Trace Length – MCH to DIMM3
2.1” to 10.0”
Trace Length – MCH to DIMM4
2.1” to 10.0”
MCH Breakout Guidelines
5/5, < 500 mil
Length Tuning Requirements
CMDCLK to CMDCLK#: ± 2 mil
CMDCLK pair to pair: within ± 4.0 in.
CMDCLK pair to DQS pair: ± 1.75 in.
CMDCLK pair to Source Clocked Signal: ± 2.0 in.
Figure 6-7
Figure 6-6
Figure 6-9
Figure 6-7. Command Clock Topology
DIMMs
CMDCLK0 & CMDCLK0#
MCH
CMDCLK1 & CMDCLK1#
CMDCLK2 & CMDCLK2#
CMDCLK3 & CMDCLK3#
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 ...