Re: gEDA-user: Implicit or Explicit Power Pins

[sdb@xxxxxxxxxx (Stuart Brorson)]

> 
> Hi,
> 
> I just started using gEDA and need some guidance. 
> 
> The Gschem FAQ says to always make power pins explicit:
> 
> http://www.geda.seul.org/dokuwiki/doku.php?id=geda:faq-gschem
> 
> The geda net= mini-HOWTO says that implicit power pins are recommended:
> 
> http://geda.seul.org/wiki/geda:na_howto

Hmmm.  This ambiguity in the documentation is not good.  It exists
because different people wrote different sections at different times.
Each person wrote something which reflected their design philosophy.
My philosophy (reflected in the gschem FAQ -- which I wrote) is to
always expose power pins.

> I'm making a board that uses the ATMega8 and would like to put 
> decoupling caps on the Vcc.  How do I do this if there is no Vcc pin on 
> the symbol?  Do I need to add pins myself?  If the consensus is that 
> explicit pins are generally the way to go, is a push to update the 
> library being made?

Here are possible things you can do:

*  Redraw the symbol.  Yes, it's a PITA, but part of doing designs is
drawing symbols.

*  If the symbol has implied power pins (net= attribute), then just
stick your decoupling cap on the same schematic sheet and attach it to
your power net and GND.  To attach to the power net, just draw a net
from the cap, and then give the net a netname= attribute.

> Seems like everybody could be happy if power pins could be included in 
> all the symbols, but then easily hidden or shown by setting an attribute 
> on the symbol itself...

Another way to work this problem involves creating hierarchical
blocks, in which an abstracted version of your symbol is placed at the
top level, and the full drawing of your part is placed on a
push-through schematic.  However, gEDA is still weak w.r.t. hierarchy,
so this method is not recommended.

Stuart