74
Memory Controller
Table 35.
Source Synchronous Routing Recommendations
Parameter
Routing Guideline
Reference Plane
Stripline: Route over unbroken ground plane
Microstrip Routing: Route over unbroken power or
ground plane
Preferred Layer
Stripline
Topology
Stripline (stubs needs to be <250 mils)
Breakout
5 mils x 5 mils Maximum length of breakout region of
500 mils.
Strip line Trace Impedance
45 ohms +/- 15% OR 50 OHMS +/- 15%.
Strip Line Trace Spacing (trace edge to neighbor trace
edge)
•
5 mils spacing acceptable between pins and
breakout regions
•
>12 mils edge to edge between any DQ/DQS
signals
•
> 20 mils (edge to edge) maintained from any
other groups
Trace Lengths
Refer to DIMM DQ/DQS Topology
DQ Group Spacing
Spacing from other DQ groups 20 mils minimum
Series Resistor Rs
22.1
Ω
+/- 5%
Parallel Termination
•
Single VTT termination of 51.1
Ω
+/- 5% to VTT
(1.25V)
or
•
Split terminations of 100 ohms +/- 5% to 2.5V and
100 ohms +/- 5% to ground.
•
Place the VTT termination in a VTT island.
Length Matching Requirements: within DQS Group
+/- 0.050” within DQS group
Length Matching Requirements: All DQ/DQS lines to
Clock
•
The package lengths from Die to Ball provided in
must be accounted for when length
matching
•
When M_CK is routed on a stripline layer, DQS
should be routed to /- 1.5” of its
corresponding M_CK
•
When M_CK is routed on a micro-strip layer, DQS
should be routed to /- 1.0” of its
corresponding M_CK
Routing Guideline 1
Route all data signals and their associated strobes on
the same layer.
Routing Guideline 2
Minimize layer changes (two vias or less)
Routing Guideline 3
Do not share series terminator resistor packs between
DQ/DQS and Address.
Number of Vias
2 (Equal number of vias between DQ and its
respective DQS signal)
Summary of Contents for 80331
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