At 04:30 PM 2/4/01 +0000, Steve Wiseman wrote:

>On Sun, 4 Feb 2001, David W. Gulley wrote:
> > If you are designing a power component (e.g. packaged DC-DC converter)
> > with multiple power pins and define them as output, then you get an
> > error that multiple output pins are connected. If you define them as
> > input, the net has no driver.
>I'll take having to place a No-ERC in that circumstance. It's a conscious
>decision, and I think that tying drivers together _should_ be alerted.
>Protecting me from myself is what I pay the ERC for...
>So - good point, but not going to stop me doing this.

I'll agree. Multiple power *output* pins is a relatively unusual 
circumstance and it is easy enough to pop down No-ERCs. The fact that power 
nets are not checked for a power source is a routine problem. I've seen 
plenty of schematics without one.

However, my modification of the idea is simply to change power-input pins 
to inputs. Power outputs would be left as power * or changed to outputs. If 
there is any power pin or output pin in a net, the net will be recognised 
as correct.

It seems to me that the difference between power and output is that 
multiple power pins may coexist in the same net. The other difference is 
that the net may be expressed with a power port. If any power port is used, 
or any power pin our output pin is in the net, (or certain other 
combinations as determined by the error matrix), it is considered driven, 
and inputs will not report an error.

It is a bit problematic, however, to go outside the standard libraries. It 
can make communication with other designers more difficult. In this case it 
would seem to be harmless if some parts with power-in pins represented as 
inputs were converted by another designer to power pins. All one would lose 
is the special ERC facility, i.e., back to where we are now....

Abd ul-Rahman Lomax
PCB design, consulting, and training
Protel EDA brokering (resale) services
Sonoma, California, USA
(707) 939-7021, efax (419) 730-4777

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