No-Connect Inconsistency

[jmk]

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.

[paulvdh]

@jmk

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.

[jmk]

@paulvdh

Unfortunately I am having some troubles with the nightlies at the moment,

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.

[gkeeth]

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)

[paulvdh]

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.

@gkeeth

This also doesn’t make sense with the pin conflict matrix,

But just excluding the pin from the netlist does not make sense to me.

Edit: Removed some text that was faulty.

[gkeeth]

@paulvdh

Another interpretation is: Nothing is connected to the IC internally (For example there is no bondwire from the IC pin to the IC.) And in this last case, you could make use of this by making the pad part of some other net to route an extra track under the IC.

This is the “free” pin type

[jmk]

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?

[retiredfeline]

[SOLVED] What is Electrical Type `Free` used for?

I just realized that there is a new entry in the electrical type drop down menu. Do you know what the purpose of Free is? It’s not yet present in the official Eeschema documentation so it must be pretty new. [image]

[jmk]

Thanks @retiredfeline , but the below comment by @craftyjon doesn’t help much.

@craftyjon

The other way to think about it is that “Free” pins can be routed through if it’s convenient on the PCB. There may also be “no connect” pins where it’s a bad idea to connect anything at all to the pad. But, for cases where the pad may be connected to anything without any bad effects, it can be useful to connect it to whatever net needs to be routed through the area so that you can route across the pad.

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.

[retiredfeline]

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

[Jonathan_Haas]

@jmk

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.

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.

[jmk]

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.

[craftyjon]

The industry does not seem to agree on terms for this, I have seen all kinds of terms in the datasheets. Fundamentally, the distinction in KiCad is between pins that the manufacturer says you must not connect to anything, and pins the manufacturer says can be connected to anything (such as route-through pads on large BGAs)

[jmk]

Thanks for your reply.

My reaction to first trying to understand the Kicad pin descriptions was: “What, new names, here we go again”, meaning, as you so diplomatically phrased it “The industry does not seem to agree on terms for this”.
I went looking for the Kicad definition for these names and found nothing.

All is well now after @Jonathan_Haas ’ comment.

[craftyjon]

@jmk

I went looking for the Kicad definition for these names and found nothing.

Schematic Editor | 7.0 | English | Documentation | KiCad

Search “pin electrical types”

[jmk]

Thanks, those descriptions are mentioned in a post of yours I quoted earlier in this thread.

I don’t like some of the descriptions. I have plenty of time, you haven’t. I’ll give it some thought and PM you.

[craftyjon]

@jmk

I’ll give it some thought and PM you.

Better to open an issue on the docs repository, it will probably be someone else who edits that documentation

[jmk]

Will do, thankyou.

[gkeeth]

Yes, it will be me