[Solved] Meaning of "U" Line in KiCAD .sch file

[tobias24]

Hi,

does someone know, what exactly the meaning of the U line in the .sch files is?
The documentation only tells something about which parameters it has (“U N mm time_stamp”).

U is meant literally
What is N?
What is mm?
Ok, time_stamp is self descriptive.

Thanks for the help!

EDIT: I only saw the values 1 for N and mm. Nevertheless i can’t rely on them always being 1 if I don’t know what they mean.

[dchisholm]

@tobias24

. . . . What is N?
What is mm? . . .

I will wager that “N” identifies the particular section of a multi-section component. I can’t help with “mm”.

Do some experimenting with, say, a dual opamp (LM358) or a quad gate (SN7400) and see if you can seduce EESchema into revealing the secrets of “mm”.

Dale

[tobias24]

You’re my man! Well done Just verified this by creating a multi-section component, saving and looking at the .sch file.

Thanks!

Someone a clue with the mm?

EDIT:
The mm does not seem to be related to the multi-section components. It’s also 1 for them. Example:
U 2 1 575A8073
U 2 1 5763478C

And just if some KiCAD dev guy reads this: Please update the specifications Specs are the most important documents for (software) development.

[davidsrsb]

The obvious, dimensions are in mm?

[tobias24]

Sounds intuitive, but dimension of what? A component has many possible dimensions. And why is it always 1?

[davidsrsb]

@Andy_P

Now this gives me a thought – many microcontrollers have multifunction pins. What if one were to create alternate symbols and use the DeMorgan field to select which function is actually displayed? I suppose it gets real ugly real quick.

As anything up to about 100 pins are programmable, the number of permutations is absurd

[dchisholm]

@Andy_P

. . . mm is used to indicate DeMorgan or alternate-symbol drawing for a part. Sometimes it is useful to have an alternate symbol for something. The usual example is showing a NAND gate as an OR gate with negated inputs.

(Why mm? Probably historical.) . . . [/quote]
Does the two-character field (“mm” sted simply “m”) indicate that there could be as many as 99 different symbols for a given part?

[quote] . . . Now this gives me a thought – many microcontrollers have multifunction pins. What if one were to create alternate symbols and use the DeMorgan field to select which function is actually displayed? I suppose it gets real ugly real quick.

The next post after yours begins to quantify some of the ugliness. It’s not necessary to take the suggestion from @davidsrsb and contemplate the permutations possible with a monstrous 100-pin microcontroller. Some microcontroller pins have not just two, but three or more possible functions so even a diminutive 18- or 20-pin microcontroller has more possible variations for its schematic symbol than a mere mortal can efficiently manage.

When I did microcontroller projects I usually crafted a schematic symbol uniquely suited to that project. I not only labeled the pins with mnemonics reflecting the pin’s usage in that particular design, but regrouped pins so that related functions were in proximity to each other on the schematic.

Dale

[tobias24]

Thanks Andy_P! That’s a full explanation of my question.

Maybe someone should add that to the KiCAD specs.