I would say, from experiance, that hidden pins are not good, my advice is
don't go that route, show everything even NC pins.

With regard to power pins on multiple part components(or even large single
part components like a uP or memory). We create a 'power part' that has just
the power pins and any NC pins. This part of the component is then placed as
part of the power distribution and if a de-coupling capacitor is required it
can be placed directly on the pins of the power part of the component.

This enables us to seperate the power distrubution from the rest of the
circuit, it ensures that we have no hidden pins and simplies the schematic.

It works quite well.

-----Original Message-----
From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, March 14, 2001 1:39 AM
To: Protel EDA Forum
Subject: Re: [PEDA] Protel default Vcc hidden power pins

At 06:36 PM 3/13/01 -0600, John Lemburg wrote:
>I would like to make a brief comment about hiding power pins.  I have been
>burned.  My advice to anyone who thinks this is a good idea is don't do it.
>Show everything where nothing is assumed to be connected.  This allows
>proper identification of all bypass caps shown right where they are
>connected to the device.

I routinely use hidden power pins without a problem. But I also know that 
it is easy to wander blindly into the world of hidden pins and get burned 
fairly badly. *If* there is a single hidden power supply on the board, 
*and* one has verified that the hidden pins have the appropriate 
attributes, there can be good reasons for using them. Ideally, when we 
design parts that might be candidates for the use of hidden pins, the pins 
are placed such that they can be unhidden and used with ease and grace. Not 
all the Protel parts have been made this way.

If one uses unhidden pins for power, with multigate ICs, as a common 
example, the question arises of where to put the power pins, i.e., on which 
section or on all sections. Suffice it to say that this can be a nuisance 
in itself. How many times I have ended up with a mess because section 
numbers were changed for various reasons with a part with power on a single 
section, I don't care to count.

Something that I would try if I had time today would be to unhide the pins 
on one section of an IC with hidden power pins and connect that to a 
differently named power supply. I would expect this to generate an error or 
at least a net renaming warning if other sections with hidden pins were 
present in the design.

If so, and if one wants to be explicit, one could simply unhide one 
section, any convenient section, assuming that all the sections have hidden 
pins, and wire it explicitly. This would be very safe. If one wired it 
explicitly to a different net than the hidden net, it would generate an 
error or warning.

Thus one would have the best of both worlds.

As to bypass capacitors, it is just as explicit to place a bypass cap with 
power objects next to the part in question, and it is easier to implement; 
one can do it for a whole page at once by placing one cap and its power 
objects and copying it as many times as necessary. Since it is not actually 
going to a pin, the location is not critical.

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

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