On 06:30 PM 14/03/2001 -0800, Abd ul-Rahman Lomax said:

>At 06:07 PM 3/14/01 -0600, David W. Gulley wrote:
>>Abd ul-Rahman Lomax wrote:
>>
>> > 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.
>>
>>And as has been demonstrated so many times, one person's experience with
>>designs is vastly different from an other's!
>>
>>  A design I am currently working on has five digital power supplies
>>(5.0, 3.3, 2.5 1.8 and 1.2) as well as two analog supplies.
>
>Of course our experience differs. However, I think that if we could 
>collect statistics on the designs actually being made with Protel all over 
>the world, the majority would be single supply (or dual-supply analog, 
>which amounts to much the same thing, only it is V+, V-  and GND). Yes, I 
>also do plenty of designs which are multiple-supply, but multiple "VCC" 
>designs are more rare.

In the last 30 designs I have been part of, over the last 5 years, none 
have been simple unswitched single supply designs.  Almost all of these 
were multiple VCC designs - that is logic running at multiple voltages or 
switched.


>"More rare" can still be "common", so Mr. Gulley's experience does not 
>surprise me at all. And certainly Protel must be able to handle with ease 
>multiple-supply designs. The present hidden-pin system clearly is not 
>sufficient.
>
>Tango Schematic allowed sheetwise renaming of nets; a particular structure 
>was exempt from the net renaming warning (A power port plus a short piece 
>of track with a net label was always considered to be a deliberate 
>renaming). Thus one could assign VCC on one page to, say, +5V, and on 
>another to +3.3V. This was more flexible than what is created by 
>inflexible, global-always-when-hidden power pins.

What a nightmare!  I would be *hugely* against Protel worsening the 
situation with this concept. Goes completely against the grain of what I 
teach all the new engineers I see - the schematic *must* be as complete a 
document as possible.  It must document the design to the maximum possible 
extent.  If I can't see a pin on a schematic then as far as I am concerned 
that pin does not exist and I do not want to see the pin on the PCB.  It is 
a simple rule and has saved the day on many designs - especially where 
there are a number of people/companies involved. Individual designers can 
do what they like - until they walk through our door.

Ian Wilson

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