Re: gEDA-user: GND vs. PGND

[Dan McMahill <dan@xxxxxxxxxxxx>]

Stuart Brorson wrote:
> This almost smells like something which should go into the wiki.....
>
> > I used both (analog) GND and PGND symbols in my layout.  Now after
> > running gschem2pcb and loading the netlist file I see that those symbols
> > create two separated nets.
> >
> > Still I want to connect GND and PGND somewhere in my layout without
> > making the DRC complain.  I tried to add a connection between GND and
> > PGND in my schematic, but that doesn't help.
> >
> > So is there any way to tell PCB that those two nets are to be treated as
> > equivalent?
>
>
> Not that I know of, although the PCB developers may have an idea.
>
> Here is one suggestion.  Others may have a better idea.
>
> 1.  Lay out your board using separate GND and PGND nets.  At your
> desired connection point run the metal planes close together, but
> don't allow them to touch.
>
> 2.  Rename PGND to GND in your .sch files using a script, then
> regenerate the netlist.
>
> 3.  Reload the netlist in PCB, and connect your two planes at the
> desired connection point.
>
> > Or a way to auto-rename PGND to GND?
>
>
> At first this sounded like a job for Perl, but on second thought I
> concluded that you need to be *very* careful that a simple Perl script
> doesn't inadvertently rename other things which you don't want to
> rename.

if you're going to do that, wouldn't it be easier to just edit the 
netlist (someone please hit me for suggesting that) since you have just 
1 big entry for PGND and another for GND?  The implication is that it is 
a very simple edit (put the PGND stuff right after GND, remove the PGND 
at the start of its line and add a line continuation at the end of the 
GND pins).

The "right" way, I think is to make the connection with an element. 
Unfortunately what we don't have (or I don't think we do) is a way to 
have a shorting element where the shorting is done via copper as opposed 
to something you solder down.

I wonder if anything could be done with layer groups here?  Something 
like having a layer which has nothing but the GND to PGND short on it. 
Keep that layer out of the layer group for the whole design and then add 
it at the very end.  It would still be nice if we more directly 
supported this.

-Dan


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