Re: gEDA-user: Stupid symbol tricks

[Ben Jackson <ben@xxxxxxx>]

On Sun, Mar 01, 2009 at 01:46:40PM +0100, Stefan Salewski wrote:
> On Sat, 2009-02-28 at 16:51 -0800, Ben Jackson wrote:
> > I just spent a couple hours debugging a half-broken AVR microcontroller
> > which was due to me putting GND and "UGND" (USB GND) far apart on the
> > symbol and forgetting to connect GND.
> 
> Sorry, I can not really see the conclusion of your message.
> 
> UGND pin for USB should be near to the other USB related pins, I think.

Right, that's why I put it there.  I just happened to put the GND pin
on another corner and missed connecting it.  I made the symbol at most a
day before I drew the schematic and still managed to forget it.

> http://www.gedasymbols.org/user/stefan_salewski/symbols/AT90USB1287-3.sym

Mine is similar to that.

> Would you suggest to modify the symbols?

Well, in my case I am realizing that I made a symbol that led me to miss
connecting a pin.  I'm trying to learn from it, by keeping in mind that
if I put a must-connect pin next to a dozen "can connect" pins (port IO
in this case) I am more likely to miss it than if I put it in with all
the other must-connect pins like power, clock, config, etc.

I also assume that if I'd been more careful and used my explicit "NC"
symbol (a "graphical=1" symbol with a pin going to an "X") I would have
noticed if I'd tried to NC a GND.

And finally if I'd used the gnetlist DRC it might have squelched about
the NC pin.

> Some people prefer symbols identical to package shape , this is
> available too:
> 
> http://www.gedasymbols.org/user/stefan_salewski/symbols/AT90USB1287-1.sym

I made a symbol like that for a big FPGA.  In that case I used 'NET'
attributes to tie all the grounds and VCC and left only the IO pins.
It was an old enough FPGA to be single voltage, though.  Another sheet
I saw pulled all the power and GND pins out and floated them in the middle
of the big box symbol so they were still explicit but easily connected
with a single wire.  Hiding them all around with the IO seems like a great
way to miss them.

-- 
Ben Jackson AD7GD
<ben@xxxxxxx>
http://www.ben.com/


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