At 10:23 AM 3/14/01 +0100, [EMAIL PROTECTED] wrote:
>As chip designers tend to show
>ambition in specifying three and more power supplies for one chip, there is
>not much use in the hidden pin feature any more.

The vast majority of integrated circuits in designs which cross my desk are 
single-supply, and the majority of designs have only two power nets: ground 
and one other.

>  I would suggest to drop
>this feature completely. It is a relic from the times when a chip had a
>power supply of 5V, and that was it.

The feature remains almost as useful as it ever was. Further, it should be 
considered that there is a huge base of legacy designs which would be 
wrecked if Protel no longer supported hidden pins. In addition, the ability 
to load OrCAD schematics would be trashed.

*But* it would not be difficult to provide tools that would make the use of 
hidden pins less hazardous, or the elimination of hidden pins in a design 

For an example of the first, reports that detect the common errors involved 
with hidden pins could be generated. A power source electrical attribute 
should be created. A "Power source missing from power net" warning should 
be included in ERC. Sometimes we want to isolate a power pin from the power 
net, with an inductor, for example, but extra warnings, once we know how to 
suppress them with No-ERC markers, do little or no harm.

A warning that there are hidden power pins on a design would not be a bad idea.

For the second, consider a library of standard logic parts, the kind which 
presently have hidden power pins as the default. For some of them, it seems 
I recall, if you unhide the power pins you get a bit of a mess; they are 
not placed well; sometimes they are on top of each other. A new library 
could be created with better power pin placement. Another library would 
have versions of the parts with a power section; updating all these symbols 
would not change a schematic at all, visually, nor with respect to 
connectivity, except for power connectivity. Then a command would be 
provided "Place Unused Parts" which would scan the project for unused 
sections and pop them onto a new sheet. Thus one could convert a hidden pin 
schematic to an explicit schematic fairly painlessly.

(Actually, one could make a server or utility that would simply create 
these unused sections, modifying the cache accordingly and removing the 
hidden pins from the placed sections.)

Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433

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