Differential Pair Net Unconnected To Differential Pair Pin

Parent category: Violations Associated with Nets

Default report mode:

Summary

This violation appears when a differential pair net is not connected to a differential pair pin of a physical device.

Notification

If compiler errors and warnings are enabled for display on the schematic (enabled on the Schematic - Compiler page of the Preferences dialog), an offending object will display a colored squiggle beneath it. Hovering over the object will display a pop-up hint that summarizes the violation. A notification is also displayed in the Messages panel in the following format:

Net <NetName> of differential pair <PairName> is not connected to a differential pair pin

where:

• NetName is the name of the positive or negative polarity net in the pair (e.g. V_RX1_N or V_RX1_P)
• PairName is the name of the differential pair (e.g. V_RX1).

Recommendation for Resolution

A true differential pair pin is hard-wired for a physical device (e.g., a Xilinx Virtex-II Pro FPGA device). Although such a pin may appear with the identifier N (for negative) or P (for positive) as part of its name, you cannot make a pin differential simply by changing its name.

Use the Details region of the Messages panel to quickly cross probe to the pin to which the differential pair net is currently connected. Consider the following when resolving a violation of this type:

• If the net is correct but has been attached/wired to the wrong pin of the device, determine the correct pin and move the net label accordingly.
• If the net has been erroneously specified as a differential pair net, change the associated net label to the correct (non-differential) naming and remove the attached differential pair directive from the connecting wire.
• If the pin is, in fact, not to be used at all in the design, ensure that net label, wire and differential pair directive are removed and place a No ERC marker on it.

Tip

• Object hints will only appear provided the Enable Connectivity Insight option is enabled on the System - Design Insight page of the Preferences dialog. Use the controls associated with the Object Hints entry in the Connectivity Insight Options region of the page to determine the launch style for such hints (Mouse Hover and/or Alt+Double Click).