A recent thread on this forum has exposed this inconsistency.
The higher No-Connect sign is generated in the pin editor of the Symbol Editor.
The lower No-Connect sign is generated from the RHS select menu of the Schematic Editor.
The inconsistency is the Symbol Editor generated N/C pin allows the automatic “Start wire” tool to show when hovered over, whereas the Schematic Editor N/C requires the “W” (wire) select tool to attach a wire.
This occurs in 7.0.7 and 7.99
Should this be so?
IMO if a pin is marked as no-connect in one way or another it shouldn’t allow automatic start of wiring.
Personally I’d expect the NC pin type to allow you to start a wire from it, but generate an ERC error if you do so (assuming the default pin type connection matrix settings). Is that what happens?
Personal opinion: the Symbol Editor N/C pin should act as the Schematic Editor N/C pin. ie. allow a wire to connect but not offer automatic.
I don’t know how ERC handles this, never connected wires to N/C pins.
Is this inconsistency worth a bug report?
Is it too insignificant to warrant any action?
I do not see it as an “inconsistency” at all.
They are two different things and they should look different.
The “No Connect” pin in the symbol editor is for marking pins to which nothing should ever be connected. Some IC’s may for example have some pins broken out, that are only for in-house factory testing.
The “No Connect” flag in the schematic editor is a reminder for the designer in the circuit that a pin is not needed in a particular schematic and is therefore left open on purpose.
Hi Paul,
I was not questioning the style of the markings, I was questioning the different methods of attaching wires to the N/C pins.
One has the automatic start wire feature, the other needs the W to start a wire.
Why?
You went through the trouble of creating this thread, modifying a capacitor to make a screenshot and drawing the wire and doing ERC is … ???
I made a little test project and ran ERC:
And ERC shows:
So there is no warning nor error abut the Unconnected Pin at all (Looks like a bug) but it does show a warning about the No Connection Flag (Which is correct).
Schematic Editor / File / Schematic Setup / electrical Rules / Pin Conflicts Map does show it should be flagged as an error.
.
Edit: I updated the project and it now has a PCB too:
2023-08-31_asdf_No_Connect.zip (7.5 KB)
As for this other thing:
I do not really see it as an inconsistency.
For KiCad the “Unconnected pin type” is treated as any other pin (which is debatable in itself), but when a user has put a No Connect Flag on a pin, then the pin has a connection made by a user and the auto wire function is disabled.
This thread came about because because I made a mistake of reading an “Unconnected” pin as a “No-connect” pin.
Your last post made me realize my error.
Consider the matter and thread closed.
Euhm no, no really.
The No Connect Pins not getting flagged by ERC looks like a bug that should be reported on gitlab. Unfortunately I am having some troubles with the nightlies at the moment, and my Linux Mint box insists on running a nightly dated 2023-06-12 at the moment, and *&^%$#@! even the Copy / Paste of the version info does not work. (But screenshots do).
So it would be nice if someone can check / verify this in a current nightly, search gitlab and create an issue if it still has not been noticed.
And I’m now having trouble staying awake.
I’ll look into this thoroughly on 7.0.7 & 7.99 tomorrow and place a bug report if needed.
I’ll leave a result of findings here .
Goodnight for now.
I put together a different example with just a single resistor, with one pin of type unconnected and one passive pin (7.0.7)
This shows that the unconnected-type pin doesn’t count as a connection in the netlist. I guess that would make sense if the unconnected pin type is supposed to represent a pin that isn’t physically connected to anything inside the chip, but that’s what the “free” pin type is supposed to be. This also doesn’t make sense with the pin conflict matrix, where the unconnected pin type is supposed to conflict with anything, but it can’t conflict if it’s not in the netlist.
Test project:
unconnected_pin_erc.zip (3.3 KB)
I updated my uploaded project to include a PCB too, and I can verify that the Unconnected Pin is just not a part of the netlist.
But just excluding the pin from the netlist does not make sense to me.
Edit: Removed some text that was faulty.
This is the “free” pin type
This is interesting.
A “Free” pin is defined as a pin with no internal connection within the chip.
An “Not-connected” pin is a pin on a symbol on a schematic with no connection.
What is the definition of a “Unconnected” pin on a symbol?
Thanks @retiredfeline , but the below comment by @craftyjon doesn’t help much.
The comment doesn’t really give a Kicad definition of a “Free pad” or an “Unconnected pad”. I should add “Unspecified pad” to the list also.
Maybe Craftyjon, or someone else who knows, can give a Kicad definition for these three pins.
If you look at the default ERC pin conflict map, you will grok it.
Unconnected type hates every type, even itself
Free type gets along with every type
Passive type only differs from free in not liking Unspecified
Unspecified type warns about every type, except Free
The definitions aren’t very clear but I hope this helps:
Free: The pin isn’t connected to the chip and can be freely connected to whatever you want.
Unconnected: The pin is specified be unconnected, i.e. any connection is likely an error.
Unspecified: The pin maybe does something, but the data sheet doesn’t say what it does, so you shouldn’t connect it to anything (apart from free pins, which have no internal connection themselves).
I can see how especially the difference between “Free” and “Unconnected” might be confusing, when free pins are unconnected to the chip and unconnected pins are probably connected somehow but disallow an external connection.
Thanks Jonathan,
That’s the best reply to date.
I don’t use ERC, however I do like to understand any terms I read. Kicad is generally very good for descriptions and explanations, but these terms for pins I found confusing.
I’ve read Data Sheets over the years that generally show a pin not internally connected as “Unused” rather than “Free” and "Do Not Use"or “Do Not Connect” instead of “Unconnected” and “Undefined” rather than “Unspecified”.
So now I will just mentally translate to what I’m used to. 
