At 11:20 AM 12/19/2010, you wrote:
Rick Collins wrote: > If I understand correctly how subsheets > work, I can see where you might want to display to the user a given > subsheet only once rather than separately each time the sheet is > referenced. Not sure, if I understand what you are aiming at. One of my current projects involves a subcircuit that needs to be repeated 69 times. With subsheets I don't need to have 69 times the same schematic in the documentation. If I have to change some aspect of the subcircuit, I don't have to apply the change 69 times. So for this particular project the way geda treats subsheets is a real work saver. :-)
But it is a problem with documentation. You have one page in your schematic and each part has a ref des. In your example, on the board each part in the subsheet has 69 instances, all with unique ref des. If your ref des is hierarchical (subsheet/refdes), then the ref des tells you what instance of the sheet to consider. But if the tools generate new ref des that are not hierarchical, then you need to at least be able to view each subsheet separately, with each instance having its own ref des. This does not mean you have to edit 69 pages when you make a change. If the tool actually "understands" subsheets as hierarchy to be instanced, then it should allow you to edit the original subsheet once, but allow you to view it N times, each with the component ref des that will be used in layout. It may make it hard to figure out which subsheet instance to view in the schematic. With the hierarchical ref des it tells you which instance. With component renumbering you have to search to find the right sheet... the same as non-hierarchical schematics.
> Does it make sense to let the schematic package reassign > ref des in multiple instances of a subsheet? IMHO, this is the job of gnetlist. On schematic level multiple instances should be exactly the same. That's why they are instances rather than copies.
There is more than one way to view instantiation. You don't have to "see" it as the exact same, single sheet. If you do, there is no way to have your documentation in step with the actual board produced... The way you are viewing subsheets, they are macros and the schematic is a programming language. A schematic is intended to be documentation and each page has to show the ref des that appears on the final product. If you push this off to gnetlist, you no longer have a one to one correspondence between the schematic and the board. It just requires a "smart" schematic package that "knows" how to assign ref des.
The only fly in the ointment is back annotation. It is common for layouts to dictate ref des based on location to allow finding parts easily. I guess there is no reason that back annotation should be hard, but in a hierarchical schematic it may require special attention.
Rick
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