Differential pairs setting are changed automatically

Dear experts
I am trying to route differential pairs in pcbnew with Kicad5.
I have already done it with Kicad4.0.7 and everything was fine,
Here, I encounter a strange behavior :
I define the diff-pair options (width 0.15 mm and line spacing 0.30 which should give 96 Ohms with my PCB stack) in the corresponding menu and if I recall the menu, the numbers are still there.
The point is when I start the differential routing, the setting is changed automatically to 0.2mm/0.25mm. And these numbers have replaced mine in the option menu.

I have used these numbers earlier in the project and I don’t understand from where they are recovered…
If someone has an idea, he is welcome.
Thanks in advance
Best regards

I haven’t done diff pairs recently, but I did notice diff pair settings in the netclasses. Did you set that to what you want? (I’m wondering if the netclass settings over rode your manual settings.)

1 Like

You get the point !
I have never noticed that the diff pairs were also in the net class.
It seems that it overwrite the manual settings when you ask for diff-pair routing.
I have not noticed this behavior in 4.0.7… But perhaps my manual settings were exactly the net class setting.

Many many thanks
Best regards

1 Like

I honestly don’t remember if the diff pair settings were in netclasses for 4.0.7. If they were I never noticed because I always set it manually and was constantly annoyed that the manual settings didn’t seem to be preserved over different sessions.

Once I have to do diff pairs again I look forward to the setting to be in the netclass settings.

Marc, are you using a nightly build? That was a known bug in 5.1 (https://bugs.launchpad.net/kicad/+bug/1782971), but I don’t think it existed in 5.0.

(If you are using a nightly then just get a new one --it’s already fixed.)

I fear that it is with a official release :
I will nevertheless make a try with a nightly build

Application: kicad
Version: 5.0.0-1.fc29, release build
wxWidgets 3.0.4
libcurl/7.59.0 OpenSSL/1.1.0h zlib/1.2.11 libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.4) libssh/0.7.5/openssl/zlib nghttp2/1.32.0
Platform: Linux 4.17.9-200.fc28.x86_64 x86_64, 64 bit, Little endian, wxGTK
Build Info:
wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
Boost: 1.66.0
OpenCASCADE Community Edition: 6.9.1
Curl: 7.61.0
Compiler: GCC 8.1.1 with C++ ABI 1013
Build settings:

There is another issue linked to this bug :
It seems that the spacing requirements put for the differential pairs applies also if you try to route a single track of the pair (for instance when you extract the signal from a pad of a chip, or when you have to put some vias before routing the diff pair).
I realized this because it was impossible to route a single track of a diff pair from the pad of an ADC with 0.5mm pad spacing. This was not compatible with the diff pair routing specifications.

This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.