Issue link: https://iconnect007.uberflip.com/i/1153097
80 DESIGN007 MAGAZINE I AUGUST 2019 for that test. By clicking on a specific occur- rence of a violation within the spreadsheet tab, the tool will jump to the exact location of that error on the PCB design (Figure 3). Any parts or traces associated with that violation will be highlighted. With tightly linked layout and DRC interfac- es, the violation data from the DRC client will automatically load into the PCB layout tool. This allows designers to easily make any nec- essary changes to their layout without having to manually cross reference between tools. To ensure that violations are cleared once changes have been made to the design, the linked DRC client can be used to run, or rerun, any selected rules from directly within the layout tool win - dow. This feature is shown in Figure 4. Testing Differential Pair Symmetry With DRC The BeagleBone Black design contains a number of differential pairs, two of which have a 90-ohm differential impedance. These 90- ohm differential pairs have been structured in- side the layout tool's constraint manager to be contained within a separate constraint class. Due to the tight integration between layout and DRC, the constraint class definitions cre- ated within the PCB tool will also be defined automatically within the DRC tool. In DRC, de- signers can quickly create an object list from the constraint class, allowing them to selec- tively choose to run the next rule on only those two 90-ohm differential nets. When designing differential impedance trac- es, symmetry in the length, spacing, and via count/positions of the pairs is imperative for proper functionality. The differential pair rule will check whether these properties are consis- tent within the proper bounds for all trace seg- ments on a given net. The overview page for the differential pair rule with the user-defined object list selected in the properties area can be seen in Figure 5. Figure 5: The differential impedance rule in DRC checks for potential impedance violations on differential traces. Rules can be selectively run on specified nets by choosing a user-defined object list in the properties section.