Issue link: https://resources.pcb.cadence.com/i/1180278
Using Differential Pairs in Allegro PCB Editor Learn more at Cadence Support Portal - https://support.cadence.com © 2019 Cadence Design Systems, Inc. All rights reserved worldwide. Page 26 Troubleshooting Issue 1: Some Differential Pair Nets Do Not Slide Together I have many differential pairs set up with three components assigned to the nets. Some parts of the pairs will slide in tandem as expected, while others will not slide together. The pin pair matching function for differential pairs gathers as much data as possible on the nets (including component class and pinuse information) to try and determine the correct set of pins to match. If a coherent set of driver/receiver pins can be determined, side branches of the net are also included. But if the data is ambiguous (no explicit driver/receiver pins), the matching code falls back on the longest path that does not include the side branch. This can be determined by selecting Show Element on the clines that are not sliding as a pair. If the differential pair constraint information is not shown in the Show Element window, that branch is NOT considered. For the branch to be considered, the Show Element window should show diffpair constraint information as follows: Constraint information (DPTol) R2.1 to U1.13 min= 1272.43 MIL max= 1472.43 MIL actual= 1343.12 MIL DPData: gap=8.00 (-0.01 +0.00) tolerance= 100.00; max uncoupled= -0.01 Note: If Find Filter is set to Nets instead of Clines, all branches of the net should show the differential pair constraint information to consider the entire net. If all branches of the net do not show differential pair constraint information, the missing branches will NOT be considered a pair and slide together. Solution Change the pinuse of pins on the net so there are explicit driver (OUT)/receiver (IN) pin pairs on the differential pairnets: 1. Choose Edit > Property. 2. Under the Find tab, select only Pins. 3. Select all pins in the net. 4. In the Edit Property form, select Pinuse and change to the appropriate pinuse. Note: A DRIVER pin is a pin with a pinuse of OUT, TRI, OCA or OCL. A RECEIVER pin is a pin with a PINUSE of IN.