Abd-ul Rahman,
        see my comments interspersed with yours.


Brad Velander
Lead PCB Design
Norsat International Inc.
#100 - 4401 Still Creek Dr.,
Burnaby, B.C., Canada.
voice: (604) 292-9089 (direct line)
fax:    (604) 292-9010
www: www.norsat.com

> -----Original Message-----
> From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, April 05, 2001 9:53 PM
> To: Protel EDA Forum
> Subject: Re: [PEDA] Bus nets
> OrCAD net renaming was far from elegant. One of the worst schematic 
> disasters I had to work with was an OrCAD schematic that had been put 
> together from various pages from other projects. In order to 
> get these 
> pages to work together, nets had been renamed. Only problem 
> is that it is 
> less than obvious how to control net renaming: when you short 
> two nets 
> together, the combination might take one name or the other. 
> I'm sure that 
> there is some underlying rule but it is, as I said, less than 
> obvious. 
> Then, on this project, where the nets were shorted together 
> on more than 
> one page, it happened that the renaming went one way on one 
> page and the 
> other way on the other page.

Never saw that problem in approx. 10 years of using ORCAD schematic but then
I wouldn't even think of trying what you describe. Your experience was not
renaming nets for use of a bus structure, it was renaming nets out of sheer
laziness and expediency. Although you do have to be careful how you would
combine nets, in my case I would only combine singular pairs of names across
any sheets, they would also tie together only through ports and the
hierarchy on the busses. Doing a ERC report in ORCAD one could generate a
listing of connected (shorted) nets, I would quickly check this listing to
see that only suitable pairing of signals had occurred. For example the
listing would state nets C1 and RD/W\R\ were connected, if it said C1,
RD/W\R\ and C\S\1\ were connected, then I had made some error.

> Minor confusion? How about a week of work *after* we figured 
> out what was 
> going on, and still some stuff got by us. No, Protel does not 
> support net 
> renaming, or, at least, an error is generated. Like any 
> error, it can be 
> suppressed. Not a good idea.

        You are comparing a bad experience with a complex tangled mess
against my orderly and controlled methodology. Not exactly a fair
comparison. Obviously you didn't use the ERC facility to check your
interconnections either, although in this case it was obviously such a mess
it probably wouldn't have helped you. With your experience of a mess as
awful as this sounds, I don't blame your reaction but don't bleed all over a
successful disciplined use of similar functions.

> Consider what has been suggested, as I understand it. One 
> could take a set 
> of control signals, say WR*, RD*, etc., and rename them 
> CTRL1, CTRL2, etc.
> One could then take these signals off the sheet using a bus port 
> CTRL[1...]. Now, my question is, "Why is this superior to 
> simply taking WR* 
> and RD* off the sheet?" Sure, the sheet entry will take less 
> space on the 
> sheet symbol, but you have to add the renaming net labels, 
> plus ports, and 
> then, in order that the schematic make sense, one must rename 
> the CTRL 
> signals back to their original names on the other sheets. Or 
> the reader 
> will be face with wondering, "Now, was WR* CTRL1 or CTRL2?"
> Why not just place a port on the wire in the first place, 
> called WR*? And 
> another, RD*, etc.

        Simple, in some cases you would have 30 - 40 various control signals
drawn around various sheets and connecting sheet to sheet. Why do you BUS
data or address signals? For simplicity and clarity, easy to follow
connections without 20 - 30 criss-crosses or bends and joints where your eye
wonders onto another connection and to save sheet space. By your argument
above, I would take it that you don't bus data or address signals? I don't
think so. The reasons for doing this was a simple extension of the same
reasoning for bussing data or address signals.

> Numerical buses are useful and not confusing because we know 
> what nets are 
> associated with the bus, at a glance. There is no mystery. 
> Allowing random 
> names to be associated with a bus would either introduce 
> confusion aplenty, 
> or it would be a bicycle for a fish, that is, if sufficient 
> signs are given 
> to make the bus names clearly known, you could accomplish the same 
> information with the same number of object or fewer.

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

        It is clear that you just don't understand this concept, what is
confusing about a small netlabel just before the signal enters the bus, used
only to configure the signals in a manner such that they can be bussed? Then
when it breaks out of the bus, another small netlabel which breaks it
correctly out of the bus structure. Then a little further down the net is
the proper netname as usual, be it RD/W\R\ or whatever. You simply ignore
the C1, C2, etc., where it enters the bus named C1..#. I used this system
for years and years across several employers, not one person ever had a
problem or issue with it, not even the stupidest engineers or techs I have
ever worked with.

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