At 11:26 AM 2/28/01 -0600, David W. Gulley wrote:

>  Similarly, not understanding and validating the ERC errors
>  is just like not reviewing the DRC errors.

The reality of today's design environment is a perception that there is no 
time to fix all those phony "errors."

The old canard is "There is never enough time to do it right, but there is 
always enough time to fix it later." Of course, sometimes it is actually 
true. It may be better to send out the files today for a 1-day turn 
prototype and clean up the mess later.

On a prototype one might well accept cuts and jumps, while, at the same 
time, another is cleaning up the design. I've once saw a company fab 
$10,000 worth of boards instead of waiting a couple of days for the next 
revision, knowing that they would probably scrap the first lot, simply 
because they needed a functioning product immediately.

On the other hand, that company went out of business shortly thereafter. 
Probably a coincidence. :-)

I've also did a board capture and revision for a product that had been done 
perhaps ten years earlier, on an unknown CAD system and all the files were 
gone and the films discarded. My first task was to make a Protel file that 
was an exact replica of the original. In doing so, I uncovered a number of 
schematic errors. It is clear that the original board was not checked 
thoroughly to its schematic. Now, this board went into an elevator 
controller and was installed all over the world. It worked, obviously. But 
one of the errors left an open CMOS input. That's the kind of thing that 
can cause mysterious intermittent errors. Or maybe even a single incident, 
when someone stands with their cell phone close to the controller....

It is ideal, of course, to identify and correct every schematic error so 
that the ERC is clean. Open input warnings, once one has verified that the 
pin is intentionally open, should be suppressed with a No-ERC Directive. 
When I am drawing schematics, as soon as I place a part with a deliberately 
open pin, I place the directive on the pin's active spot .

Sometimes there is an error or warning that can be difficult to eliminate, 
and the project still needs to be done. Once the net list is verified, it 
may be acceptable to suppress the error. But in the long run, it would be 
best to find out why that error was reported, and fix it, if possible.

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

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