On 09:04 PM 8/04/2001 -0700, Abd ul-Rahman Lomax said:
>So, why not just draw this control bus? What one would have would be net 
>names like RD* and WR* implementing connectivity, and a bus line, which 
>might or might not be named, showing them as being organized together. At 
>the end of this bus, presumably on the left side of the page if the 
>signals are driven off-page, or on the right if they source on the page, 
>there would be a block of ports with the names of each net, one to a port.
>So a sheet symbol on the next level up would show a block of these ports; 
>they would presumably be placed together; perhaps another cosmetic bus 
>line would be drawn on that sheet.

I do this - it is not ideal but it works for now.  There could easily be a 
better method though - read on...

>The point I am making is that if you want a bus line for clarity, by all 
>means put one in. Thus this argument is seen to be misdirected:

On a side note: slightly inflammatory words there -  "misdirected".  Your 
post has a bit of a feel of lecturing about it.

Anyway, I think multiple net names will always be more confusing than one 
net name - lets make the bus function more flexible rather than introduce 
an unnecessary construct to get around an existing limitation.  I, 
personally, would be against multiple net naming being supported even as an 
option.  One reason would be the possibility of mucking up the renaming so 
that nRD became nWR on one of the other sheets through some not-so-careful 
copy and paste.

I *would* like the ability to collect multiple non-bus signals into a 
"collection".  A collection of nets would simply be a named list of 
nets.  Currently it is the bus net label (ADDR[0..31]) that carries the 
connectivity.  I would like the bus entries and the bus wire to assume a 
greater role such that the bus knows what nets it is carrying by knowing 
what bus (collection or whatever) entries have been made to it.  Then the 
net label is simply an alias for the list of nets.  The list is produced 
automatically by the netlister by noting what nets made a valid connection 
to the collection.  A bus would simply become a special case of a 
collection.  So now I can have a bus-sort-of-thing labelled ControlBus, or 
I2CBus and use it to pass this collection of nets around without cluttering 
up the top level hierarchy or the left and right edges of my schematics.

Allowing net classes to be defined in Sch would possible also allow an 
alternative method of creating named collections (this time the list of 
nets in the collection is being created manually).  (Would it be an ERC 
error if a net not belonging to the class
attempted to connect to the collection?  I think yes.  If the collection 
name corresponds to a net class then only nets in that net class can 
connect to the collection  without generating an ERC.  This gets us further 
along the way to a rules based Schematic editor.)

I can't imagine that this would be that hard to implement - it is along the 
lines of something I requested (verbally) many years ago.

Ian Wilson

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