Advanced PCB Layout Course - Lesson 4 - Max Uncoupled Length

[milos.stankovic]

Hi,
I am not sure should I post questions on this Forum regarding Advanced PCB Layout Course, Lesson 4 or not. Anyway, my question is:
When setting up Rules for DIFF90 and DIFF100 differential pairs, we set up Max Uncoupled length to 0 mils. Also, in Preferences we set up that this be reported as en error.
My problem is that it doesn't happen. I made on purpose distance between DRAM_CLK0_P and DRAM_CLK0_N to be 0.14 mm instead of 0.16 mm and DRC reports nothing (this is activity shown around 33th minute of Lesson 4). I use AD17.

Best regards,
Milos

[robertferanec]

It is sometimes stuck. Try run DRC again, or switch OFF and ON Altium. It should work. Let me know then.

[milos.stankovic]

I tried same file iMX6_Rex in AD16, AD17 and AD18. It works only in AD18. I tried one of my designs in AD17 and AD18 and it works only in AD18. I attached settings in AD17. In AD18 if I check only Violation Details it still works.

Regards,
Milos

[robertferanec]

Hmm, I know, that it has happened to me couple of times (the uncoupled length error was not visible), but I always tried to change something and then it worked. But I do not really remember what made it work

[milos.stankovic]

Ok

Regards,
Milos

[milos.stankovic]

Hi Robert,
I think I found out what is the reason for AD17 not reporting max uncoupled length when routing differential pairs.
On the pictures are shown Design Rules for diff pairs. When I make a distance between P an N wire bigger on purpose and then run DRC, no mistake is reported. I then open Design Rules and just change the priority order of DIFF100 and DIFF90 routing rules. When I close Design Rules on-line DRC is being run again (I guess because I made a change in DR) and white color is then present on the place of uncoupled length.
In AD18 everything worked ok.

Best regards,
Milos

[robertferanec]

Thank you milos.stankovic for sharing this

[milos.stankovic]

Priority of rules DIFF100 and DIFF90 is not important. It is important to swap them, to make a change in Design Rules so that online DRC is run again. Only than max uncoupled length works in AD17. In AD18 there is no problem with this feature.

Regards,
Milos