At 05:58 AM 12/21/2003, Rene Tschaggelar wrote:
Laurie Biddulph wrote:

Is there any recommended method in Protel 99 of handling the power pins on logic chips similar to my first method above that Protel 99 can handle comfortably?

Let me advocate my preferred method. I have the schematic symbol identical to the footprint, the powerpins visible. What the powerpins concerns I tend to work with netlabels, so the schematic is not cluttered with useless wires. The advantage is the ease of debugging with the scope probe. The schematic is sufficient.

The schematic is sufficient in either case (i.e., physical layout or functional symbol); likewise either case generates net lists perfectly well. (This is a separate question from power pin visibility, since power pins can be visible with functional symbols, in several ways, as have been discussed.)

However, certainly, having a symbol topologically the same as the footprint makes it easier to identify pins on the physical part, hence Rene's comment. But there are other ways of acheiving similar results, maybe a little paint -- or silkscreen pin legend -- on the PCB.

And many times I've read a schematic with such footprint symbols and it *really* slows me down in terms of understanding the *function* of the part in question, and thus where a tech would want to probe. Is it an input or an output? How do the signals flow across the page? If you've got a pile of logic, i.e., inverters, nand gates, etc., it is next to incomprehensible if you don't use functional signals; only if there is bus logic, with the pins being physically laid out in a rational sequence, does it make sense to use footprint symbols.

Three functions of schematic:
(1) Generate net lists and part lists
(2) Explain circuit operation
(3) Identify part and pin functions for debug/repair.

A quick and dirty schematic often falls short with function 2, and function 3 is impaired much more if circuit operation is not clear than if the tech has to do a little translation of pin locations. If pin locations are not really obvious, why not put a non-electrical diagram on the schematic showing the pinout? Best of both worlds!

(Likewise, pin 1 indicators are de rigeur on the PCB, even if you don't have a silkscreen on the board, and if there *is* a silkscreen, adding some pin numbers on large parts can really be a service to a tech....)

The small overhead in manually swapping the wires for re-
assignment is considered worth the effort.

Ing.Buro R.Tschaggelar
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