Auto router does not use whole net, only looks at pin pair in order they were added to database. No setting I know of to prevent. Look up reschedule command to reduce up front. I use auto router as much as possible and just review for this stuff and fix manually. Other designers refuse to auto route for reasons like this.
Thanks for the answer but your assumption is a little unbeliveable. The router knows a net what it wants to route. And it knows all the pins connected to that net. So when it connects a pin to that net, it needs to find the way to ANY pin on that net, the shortest one. This is much more credible assumption, just because its easy to solve this task in an algorithm. Why would restrict the search for pin pairs, if its easy to search all pins on the net anyway ? There is no reason to do that. When you click in the project window on a net it will highlight all component pins on it.
What would be the purpose (advantage) of that limited "pin-pair routing" ? Time? I don't think so. I have time. The router solves an 5'' x 5'' 2 layer board less than a minute. I would wait for 10-20 minutes if it would create better routes, wouldn't you ? By the way I checked the pin-pair ( right-click, "Select Pin Pairs" , then click on the leftmost optcoupler 3rd pin , the pin after the route turns back) . That pin 3 is paired to the 2nd optocoupler's pin 3. (the 2nd pin to the right). So pin-pairing doesn't explain that long loop.
I agree that is the way a person thinks. I don't believe the program does a search for nearest pin during routing. Only during length minimization. The reason I believe this is many times I see a fan-out on two sides of the same pin. Each belonging to a different pin pair. I have also seen it loop a pin pair around three sides of the board when it had a straight shoot to another pin on the same net. I also work with asc files a bit and find PADS stores route data under pin pair header. Sometimes reading in asc file will result in trace on top of trace if shared between two pin pairs.
I think they are doing this as a easier programing method. Some nets get routed in fixed order, some best fit. By routing pin pair order they have both covered with same code, assuming all pin pairs are already defined. Searching for pins on same net would mess up dedicated flow. Example starburst routing from virtual pin has to be routed by pin pair to avoid bypassing virtual pin if looking for nearest pin on same net.
I would love better auto router. I write basic programs now and looked into what it would take to write one. Found different strategies on the web and saw it was way above my skill level.
Maybe you're right.
But this: "I think they are doing this as a easier programing method" - sounds very bad. You know that the most basic PADS system costs 5k USD. A full system is near 20k. And they are looking for easy job ? Hmmmm.