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Re: Best practice for multi-gate symbols ? (74LVC2G14 has hidden pins)


On 21/04/19 22:58, Henner Zeller wrote:
On Sun, 21 Apr 2019 at 13:28, Nick Østergaard <oe.nick@xxxxxxxxx> wrote:
Hello Henner,

I think the Librarians more or less communicate exclusively via github issues. So it may be worth to post this as an issue on the kicad-symbols repo over on github.
Thanks Nick; looks like this is
https://github.com/KiCad/kicad-symbols/issues/756 and is decided to be
pushed to v6.


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TlDr: The library team decided to move power pins to a separate unit for all such components.

We planned to get everything done in time for v5 but where lacking manpower to fix every lib (I think only the lib listed in this report and the ieee style libs are still using hidden power pins)


Yes it meant that these symbols no longer support the "interchangable units" feature as well as limiting spice support for these.

Another issue is that right now ERC does not check for not placed units as there is no "this unit is mandatory" flag in the current file format (i requested it for the new one but think never got an answer on that)

The alternative would have been to use visible power pins copied over all units. This however had a lot of issues during v4 (No ERC check for connecting such a pin multiple times) and still had issues with the nightlies at the time we made that decision (I think some of them are still in.) Examples that comes to mind immediately (without needing to search the bugtracker): unconnected copies are reported as unconnected.

The main reason however was that we feel it is very confusing to use a symbol that has the same pin multiple times. For everyone involved in reading a schematic that uses such a symbol (Give such a symbol to your boss without explaining this specialty first. See how long it takes them to ask why ICx is not connected to supply.)  The increased clarity and flexibility of using a separate power unit simply was worth the downsides we knew at that time. (We did not know about the simulation issue when we made our decission. I feew we would have decided the same way if we would as i feel simulation is an extensions that is not allowed to limit the core function of kicad which is making pcbs. We have specialized symbols for simulation added in the meantime to support this usecase as well. Interchangeable units are not that much of a help anyways and manual unit switch is possible even with the current symbols.)