03 - Constraint Objects

Along with constraints, you can also manage the following constraint objects in Constraint Manager:

• Extended Nets or XNets

A net represents an electrical connection from one pin to another pin (or pins) on the same device or on a different device.

If the path of a net traverses a passive, discrete device (resistor, inductor, or capacitor), then each net segment is represented by an individual net entity in the board database. The constraint system, however, interprets these net segments as a contiguous extended net, or an XNet. An XNet can also traverse connectors and cables in a multi- board configuration. Capture automatically creates XNet for nets associated with 2-pin passive components.

• Pin Pairs

A pin pair represents a pair of logically connected pins, often a driver-receiver connection. Pin Pairs may not be directly connected but they must exist on the same net or XNet. You use pin pairs to capture specific pin-to-pin constraints for a net or an XNet. You can also use pin pairs to capture generic pin-to-pin constraints for CSets. Generic pin pairs are used to automatically define net- or XNet-specific pin pairs when the CSet is referenced.

• Differential Pairs

A differential pair represents a pair of nets or XNets that have to be routed in a way that the signals passing through them are opposite in sign with respect to the same reference. This ensures that any electromagnetic noise in the circuit is canceled out.

You can create a differential pair in Constraint Manager. In Constraint manager, you can create differential pair manually or can specify setup option for auto-creation of differential pairs.

• Match Groups

A Match Group is a collection of nets, XNets, or pin pairs which must all match (in delay or length) or be relative to a specific target within the group.

• Net Group

A Net Group is a collection of various net (signal) objects. Different types of net objects, such as nets, buses, and net groups, can be members of a Net Group.

• Net Class

A Net Class constraint object lets you group net objects that share common characteristics and require a similar constraint requirement.

• Constraint Set (CSet)

A CSet is a named, reusable collection of constraint values.

Constraint Manager organizes constraints and CSets into the following domains:

• • • Electrical
    • Physical
    • Spacing
    • Same Net Spacing

You can assign the appropriate constraint set to objects in your design, changing references (or re-defining the currently assigned constraint set) as your design requirements change. A constraint set can be referenced by any number of objects in your design. CSets are not supported in the design domain.