1. Use Setup>Constraints to open the Constraint Manager, then left-click in the Electrical domain to open it.
2. In Analyze>Analysis Modes, select Electrical Modes and set the Radio Button for Total Etch Length to On and OK to close the form.
3. Open Net>Routing>Total Etch Length, scroll down through the Nets and locate the LED1 to LED4 Nets, drag select these Nets, right-click in one of the selected Name cells and Create>Class, name the Net Class LEDNETS and left-click>OK to create the Net Class.
4. Scroll to the top of the list of nets, the LEDNETS Net Class, will have been moved to the top of the list, if necessary, open the LEDNETS Net Class to display the members and right-click>Analyze on the LEDNETS name.
Now the Actual values will be filled in for the current routing, the same value will be shown in the Min and Max groups. In this case, our object is to try to match the lengths within about 0.5 mm of the longest. Your numbers may vary but, as an example, let’s say that LED4 is the longest and has a currently routed length of 34.275 mm, setting the Constraint Min to 34.0 mm and Max to 34.5 mm will be sufficient in this case.
Once you have values for the Min and Max requirements, you can set the Constraint values and apply the Constraint to the LEDNETS class.
5. Open the Electrical Constraint Set>Routing>Total Etch Length and, in the “gloss” cell, right-click>Create>Electrical CSet and name the new Constraint Set LEDLENGTH
6. Left-click on the “black triangle” in the “gloss” cell top open the constraint list and set the Min and Max values calculated above.
7. Return to Nets>Routing>Total Etch Length, locate the LEDNETS class and select the LEDLENGTH Constraint Set from the drop-down in Referenced Electrical CSet cell. The values from the Constraint Set will be filled in.
8. If necessary, right-click>Analyze in the LEDNETS cell to get the net “actual” and “required” routing lengths checked. The longest net should be fine, since this was used as the reference for your calculation but the other nets may well be outside the required limits.
(Green actual values meet the Constraint, Red actual values fail to meet the Constraint) It’s likely that the Min values will be “short”, and Red, the MAX values will all be Green since they are less than the required Max value.
9. Go back to the PCB Editor window, the Constraint Manager window can remain open so that it can be re-visited after the routing is corrected.
10. Locate the LED ROOM on the board, around middle right.
11. Locate one of the traces that does not meet the Total Etch Length requirements, there should be an “E L” DRC for the nets that need correcting. (Check that all the DRC colours are enabled in Setup>Colors if you are not seeing the DRC markers in the design)
12. Hover over a trace that needs correcting and right-click>Delay Tune (Note that the delay tune will start at your right-click point so don’t “crowd” the components when right-clicking the start!)
The routing will initially have a “tracer” through the route indicating that the Length rule is not being met and the “heads up” display will indicate “red”, negative value means “short”
Trace does not meet requirement, “short”
As the Length meets the rule the “tracer” will clear from the routing and the “heads up” display will indicate “green” “meets”
Trace meets requirement
The “tracer” will return again as the added delay increases the Length beyond the required Maximum and the “heads up” display will turn red again.
Trace does not meet requirement, “long”
13. Left-click to accept the routing when corrected.
You can add lengths that meet / don’t meet and see what the effect is in the Constraint Manager. You can also change the Delay Tune parameters in the Options tab to see what effect they have. The “gap” for the delay routing comes from the One times the Line to Line Same Net Spacing rule OR Three times the Min Line Width Physical rule in Constraint Manager.
14. You can save the board with the matched lengths, if you wish, this won’t affect any
of the subsequent labs. It’s OK to overwrite the gloss.brd.
End of Lab