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
easier.
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.)
[EMAIL PROTECTED]
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433
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