Ian Wilson wrote:

On 08:57 AM 27/07/2003, Abd ul-Rahman Lomax said:

At 09:59 PM 7/25/2003, Craig Scribner wrote:

Here's our current documentation for this. Please let me know if it's
unclear on any of the points that have been discussed.


Here are my comments, page references are to pages in the document.

p. 1. The term "net identifiers" to refer to the various relevant objects can be a little confusing. Some of these primitives do not establish a net name, rather they function like a wire. Ports and Sheet Entries do not assign any name to the net; what they do is to make a connection between primitives of the same name (in the case of Sheet Entry/Port combinations, the connection is restricted to connection between the Sheet Entry and the Port on the named sheet, not to other Ports of the same name that might be elsewhere in the project). They function just as if you ran a wire between the sheets; as you know, wires don't control the net name.

They (sheet entries and ports) can optionally name nets in DXP. In Abd ul-Rahman's very useful discussion that followed this text just remember that in DXP, Ports and Sheet Entries can, optionally, name nets.

Me, I am an untrusting soul - if I want to re-use a design I will rename nets wherever possible, and suffer the small delay it takes me to globally rename nets to conform to a new naming system, if required. More often the new project can inherit the old naming scheme and so there is little problem. It is rarer that I am merging multiple similar older designs where I have to resolve a naming conflict, so I don't worry about the effort spent doing so.

I *hate* reading schematics where D0 on one page may be something else on an another and worse, D0 on one page may *not* be D0 on another. So I will go a long way before accepting this.

I understand what you are getting at but I would say that the worst situation is where the schematics give you no help as to how many sheets have D0 on them. Letting the CAD program just connect up all instances of a net name has certainly cause me grief in the past when you have to explicitly sort through 14 schematic sheets to find every instance of a given net (and still you miss one). WHat using ports properly allows you to do is ensure the schematics lead you from sheet to sheet when tracking down a given net.

Personally I always rename nets to unique names but still I find that the full hierarchical design lead to much easier schematics for the test and fault finding guys to use because they now that if a net is not brought onto a sheet via an entry then it isn't on the sheet.

chris lowe

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