Terry,
Just could not stop myself from answering this post.
If you ask 10 engineers about how they would like to see power pins on a
schematic
or not (especially now that we are dealing with 5/3 volt parts) and you WILL
get 10 different
answers. I am a PCB designer who does not believe the schematic is just a
graphical net list
and have done the CAD library gig for quite sometime dealing with the many
engineers that
wanted to see different things. When you are trying to build a process that
deals not JUST with the
schematic but right through creating a proper bill of material automatically
from the CAD system to
am MRP system dealing with how the different parts numbers for a part that
graphically really is the same is a bit of a task. I am dealing with just
such an engineer now who can't understand how it keeps happening but (he is
using Orcad capture, and board is done in Protel) parts that want 3V get 5V
and visa versa, only because it is mot readily apparent graphically what
part is REALLY getting what voltage. If it wasn't for us PCB designers
checking the engineers work that board would never be powered up properly.
This person is a very good engineer, I am not nocking that but sometimes
engineers do not take in the bigger picture when looking at a problem, which
should include the entire
group on the food chain of data to the final product.
Sorry but that "just a graphical netlist" got to me.

Robert M. Wolfe, C.I.D.

----- Original Message -----
From: "Terry Harris" <[EMAIL PROTECTED]>
To: "Protel EDA Forum" <[EMAIL PROTECTED]>
Sent: Thursday, December 06, 2001 6:24 AM
Subject: Re: [PEDA] Using Multiple Vcc for same part


> On Mon, 3 Dec 2001 09:06:03 +1000, Matthew van de Werken wrote:
>
> >I'm the exact opposite of this. I try to make each schematic part look
like
> >its function, rather than its physical layout. That way, the schematic
will
> >be a proper abstraction of the circuit, rather than a rough draft of the
> >PCB. IMO it makes the schematic easier to read and understand if it's
> >abstracted from the physical layout of the board.
>
> And so would I but then I'm an electronics design engineer who does his
own
> PCB layouts not a PCB designer who considers the schematic to be some kind
> of graphical netlist entry system.
>
> For the same reason I will be keeping power pins hidden in most
situations.
>
> For the original poster just unhiding the power pins will result is a mess
> with overlapping annotations for most existing library parts. You will
> likely have to revise the symbols to show power pins clearly.
>
> Taking your 74VHC00 example if you do show power pins are you going to
show
> them on all 4 gates like pin 7 and 14 will appear 4 times for each
package?
> Or do you show them on the first gate so the reader seeing the 3rd gate
> will have to search the schematic for the 1st gate of that package to see
> what supply it is running from? IMO both ideas are horrid.
>
> The suggestion of a '5th' part in the package just showing power pins is
> okish but for a reader it is worse than just adding a power table to the
> last sheet listing all packages and power pin connections.
>
> I have not yet had to do a thoroughly mixed 5/3.3v system with Protel but
> if I did I would likely create symbols with hidden VCC3 and VCC5 pins and
> annotate the symbols with 3v or 5v to give the 'reader' more information
> where he needs it.
>
>
> Cheers, Terry.
>

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