[gta02-core] U490{1,2,3} diagrams

[Werner Almesberger]

Rene Harder wrote:
> different pin numbers as well.  NXP for example swapped the input pins
> B=1 and A=2 (TI  has B=2, A=1). So that means this symbol is TI specific
> anyways and would cause a lot of confusion to other people who might use
> the symbol.

Argh, right :-( So we have three dimensions of variation now:

1. pin numbers change when the number of pins changes

2. not an actual difference, but a nice source of confusion: vendor
   swaps top and bottom view (TI), some may not think this needs
   clarification (Rohm, DTC123), some have a creative solution (NXP,
   "transparent top"). I like NXP's approach.

3. permutations of the names of otherwise equivalent pins

> I see 2 possible solutions:
> 1. we switch to a more manufacture specific name (SN74xxx )
> 2. we hide the pin numbers so that this will be a generic symbol for all
> manufactures.

KiCad can associate different packages with the same symbol. In
fact, it will let you associate any package with any symbol. You'll
discover the missing pins much later, in DRC ;-)

The name sn74x1g00_5 would indeed be unique. If using vendor names
up to and including the "74", we would have a problem with 74x1g00_5,
though, since parts like STMicroelectronics' 74V1G00 would conflict.

We could of course earmark a name like nxp74x1g00_5 for NXP's part.
They seem to be the only ones who swap A and B.

I like to have visible pin numbers. This makes it easier to look up
things, without having to guess or fire up KiCad.

The more I think about it, the more I like the nxp74x1g00_5. That
would mean no changes for the rest. What do you think ?

- Werner