Instance Terminal Connectivity Considered During Extraction

The connectivity of an instance terminal can come from the schematic (if the corresponding schematic instance has connectivity) or from the first overlap detected in the layout. Once assigned, Layout XL considers the connectivity of an instance terminal as sticky, which means that when an instance terminal is assigned to a net, it stays assigned to that net unless you change it using, for example, the Propagate Nets command.

For example, assume you have an instance, I2, with no connectivity in Layout XL. When you move this instance to overlap a shape assigned to net2, Layout XL creates an instance terminal for I2 and assigns it to net2. If you now move I2 to overlap a shape on net1, a short is created.

Depending on the pin connectivity of the terminals, pins, and pinFigs of an instance, the extractor considers these connections differently.

• Strong-connected pinFigs: Two pinFigs are strongly connected when they belong to the same pin. The connectivity extractor considers such pins as connected in the master of an instance. Therefore, no shorts are reported for these pins in the Annotation Browser.
• Weakly-connected pinFigs: Two pinFigs are weakly connected when they belong to different pins of the same terminal. The connectivity extractor considers such pins as connected in the master of an instance. However, Layout XL runs additional checks to ensure no current flows between such pinFigs. No shorts are reported for these pins in the Annotation Browser.
• Must-connect pins: When a terminal is set as must-connect-pins, two pinFigs of different pins must be connected together in the design of the instance. If the pinFigs are not routed together, the connectivity extractor considers the connection as incomplete. An open marker is reported in the Annotation Browser.
• Must-connect terminals: When two terminals are set as must-connect, pinFigs of the terminals must be routed together in the design of the instance. If the pinFigs are not routed together, the connectivity extractor considers the connection as incomplete. An open marker is reported in the Annotation Browser.

The following exceptions apply:

• Where an instance terminal is assigned to a net with a must-join terminal at the current editing level, the extractor does not consider the instance terminal sticky. However, if the instance terminal is moved away from an overlap, it keeps its connectivity until the extractor finds an overlap with a different must-join net that is better suited for the connection. If such an overlap is found, the instance terminal is reassigned to the new net.
  This behavior has been implemented to support the must-join pin model at different levels of hierarchy.
• When you move a physical-only instance, which is an instance for which the lvsIgnore property is set to t, Layout XL automatically reassigns the connectivity based on any new overlap. The only exception to this is when the physical-only instance has the lxStickyNet property set to t, in which case the extractor creates a short marker if the new connectivity does not match the existing connectivity.
  If there is no new overlap after the move and the physical-only instance has the lxStickyNet property set to t, the existing connectivity is retained. If the lxStickyNet property is not set to t, the existing connectivity is deleted.

Related Topics

Supported Pin Connectivity Models

lvsIgnore Property

lxStickyNet Property

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