Re: gEDA-user: 74xx symbols

[Jim Battle <frustum@pacbell.net>]

At 03:57 PM 7/31/02 +1000, you wrote:
>On Tue, Jul 30, 2002 at 10:18:44PM -0700, Jim Battle wrote:
> >
> > Some parts, for example, the 7474 and the 74175, have complementary
> > outputs.  The symbol in the library shows one with a bubble and one
> > without, but the label near the bubble is "/Q".  Although I understand 
> what
> > was meant, it seems like a double negative.  I would label both outputs as
> > "Q" and have a bubble on the negated one.  It is clear in these two cases
> > what is meant, but being consistent is important if "bubble notation" is
> > used more extensively, especially with parts that don't have complementary
> > pins like this.
>
>Be careful here. These are different pins. Doing something that
>could connect them together (2 pins with the same name) in netlisting
>tools is a dangerous idea.

But these are just text items -- they have no use to a netlister; they are 
there just as an aid to human comprehension.  Edit a symbol (say, 
7474-1.sym); select Q, type "ee" to edit the thing, and it is just 
text.  You could replace it with the gettysburg address if you made the 
point size small enough.

I haven't tried all of the netlisters, but I tried ged and verilog and both 
of them just used the pin numbers as the pin label.  Perhaps a clever 
netlister could guess the nearest text and use that instead, but it seems 
prone to failure.  My understanding is that whenever the new library comes 
out, there will be an explicit "label=xxxx" property attached to every pin, 
allowing for more rational netlists for verilog, among others.

-----
Jim Battle == frustum@pacbell.net