82
Memory Controller
Table 40.
Clock Signal Group Registered/Unbuffered DIMM Routing Requirements
Parameter
Routing Guideline
Reference Plane
Preferred Topology
Route over unbroken ground plane
Differential Microstrip (preferred) or differential
stripline
Preferred Topology
Stripline routing is recommended for the clock signals.
Micro-strip is also acceptable with strict adherence to
all routing recommendations.
Breakout trace width and spacing
5 mils x 5 mils routed as differential pair
Microstrip Trace Width
Differential: Trace impedance of 100 ohms
Refer to
Trace Spacing (edge to edge)
5 mils for breakout
5 mils from one clock M_CK of the differential pair
M_CK#.
>20 mils between the other signals or vias including
other clock pairs.
Package Trace Length
Breakout Trace Length (TL1)
Lead-in to Connector Length (TL2)
See
<= .5”
2.0” to 10” (correlated /- 1.0” of DQ/DQS and
command trace lengths)
Termination:
- Buffered Termination
- Un-Buffered Termination
None required
22.1 ohms +/- 5% series termination on each
differential segment after the breakout.
Length matching Requirements:
The package lengths from Die to Ball provided in
must be accounted for when length matching
•
Within differential clock pairs
•
+/- 0.025” max. within Pairs [Intra-pair]
•
With respect to the DQ/DQS group (from die to
DIMM connector)
•
+/- 1.5” max. when M_CK is routed Stripline
•
+/- 1.0” max. when M_CK is routed Micro-strip
•
With respect to Address/Command group (from
die to DIMM connector)
•
For total capacitive loads greater than 36pF,
M_CK trace lengths must be 2.0” to 3.0” longer
than all ADD/CMD/CTRL trace lengths
•
For capacitive loads less than or equal to 36pF,
M_CK trace lengths must be 1.0” to 3.0” longer
than all ADD/CMD/CTRL trace lengths
•
Among Unbuffered Clock Pairs
•
+/- 0.1” max. between the 3 pairs of Unbuffered
Clocks
Series Resistor Rs
•
22.1 +/- 5% ohms unbuffered
•
no series resistor required for registered DIMM’s
Parallel Resistor Rp
•
no parallel resistor required
Routing Guideline 1
Clock signals’ polarity needs to be alternated.
Routing Guideline 2
Maximum of 2 pair of vias from controller to DIMM
Routing Guideline 3
Route clock as differential impedance of 100 ohms
with single ended impedance of 50 ohms
Summary of Contents for 80331
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