Adding The Length of Two Nets That Are Divided by a Series Element
Be aware of series resistors and similar components along the length of a tuned connection. See to it that both sides of the
series element have a name that would indicate its special use case. The two nets may need to have their lengths added
together while others in the group may or may not have a series resistor. If any, the clock needs a buffer.
We call this case an "x-net"; using this feature is part of the Cadence "high speed" routing option along with pin-delay and
other features. Another clever use for x-nets is for DC routing when there is a multi-segment loop spanning different nets
that must be kept short in total. In order to pass through design verification, the placement will have to be tight in order to
meet the routing rules that depend on pin-pairs for their definition.
Figure 3. The first net-based constraint assignment covers the ECS selection, Net Schedule, Topology, Stub Length and Layer Set. Here, upon
right mouse clicking the Analyze option, we get the full report where it shows some stubs and some wiring on an unauthorized layer. Other
electrical constraints will have different analysis options based on their own criteria. In all cases, red cells indicate non-compliance. Again, the
filter can hide all but the interesting ones for quicker resolution and verification.
4 www.cadence.com
Controlling Trace Length for Digital Circuits Using OrCAD X and Allegro X Tools
