Re: [PROTEL EDA USERS]: Problem with Power Pins

[Ian Wilson <considered@ozemail.com.au>]

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On 12:32 PM 31/08/2000 +0200, Joop Reekers said:
>Greetings,
>
>Maybe the information below is useful when you have a problem with hidden
>power pins.
>
>I saw some strange behavior on a schematic component in the Motorola CMOS
>Logic 1991 Lib.
>Using the MC14066B (MC14016B).
>I had changed the powerpins 7 (GND) and 14 (VCC) to passive pins, not
>hidden, only on part 1 of the 4-part component.
>In the schematics I connected pin 7 to net G1 (my logical ground) and pin 14
>to net VC5V.
>Made the netlist (Net labels and Ports global) of the 3-sheet schematic.
>
>After PCB-design I did the usual DRC and found short circuit errors.
>Net G1 was shorted with net GND and net VC5V was shorted with net VCC.
>
>Investigating the netlist revealed that the pin 7 was connected to nets G1
>and GND, pin 14 was connected to nets VC5V and to VCC.
>I did not even use net GND in the schematic (I use GND only for safety
>ground).
>
>Looking at the component in the Schematic Lib. Editor did not show anything
>unusual, even with Hidden Pins checked (in the lower left corner of the
>display).
>
>Tried all kind of things with editing, removing and replacing pins, updating
>schematic, removing and placing the part in the schematic without result.
>Finally I found the cause of my problem: the parts 2, 3,and 4 of the
>component contained hidden power pins!
>Normally (as far as I know) the power pins are only on part 1 of a multipart
>component.
>
>Removing the unnecessary hidden power pins solved my problem.
>
>Did more of you see similar trouble?
>
>Have a nice day!
>
>Joop Reekers
>Nedworks Almelo
>Home page: www.nedworks.nl

Hidden pins are connected to a net of the same name.  So a hidden pin 14 
with a name VCC is automatically connected to a net VCC this is what you 
are seeing.

Rant On
I have a deep hate of hidden pins.  Some on this list tell me they have 
uses.  I am only a youngster in this game (15 years) but I have never seen 
a place where hidden pins and worse, automatic net connection of hidden 
pins does anything but make life harder for everyone but the person laying 
out the original schematic.

My suggestion is to edit every sch symbol that you use and remove the 
hidden pins - make visible power pins (and make them of type POWER so the 
ERC is working for you).

Others though do offer support for Protel continuing a confusing and 
fraught-with-problems historical aspect of early computer based PCB CAD 
systems.
Rant Off

Ian Wilson



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