Re: [Xcircuit-dev] Re: xcircuit netlist->pcb

[Bryce D. <br...@tl...>]

On Tue, 23 Oct 2001, R. Timothy Edwards wrote:

> > Between xcircuit and pcb, we are really close to having a schematic+layout
> > flow for circuit boards.
>  
> That was the intention.  With me and Harry Eaton working at the same place,
> it was my hope that regardless of which program needed a change for the
> sake of compatibility, we could easily work something out.

Cool.  I didn't realize you two knew each other.


> > All the transistor models in generic and analoglib2 have letter-named pins,
> > such as B for base and E for emitter
> 
> I'm not going to apologize for being a VLSI designer.  It's what I do.  
> But it means that my netlists don't really look like your netlists, so
> you have to get used to the fact that libraries like "analoglib2" were
> really designed for VLSI work, not PCB work.  What is really called
> for here is a separate library (I should probably make it default,
> too, since more people seem to use xcircuit for PCB netlisting than
> for VLSI netlisting).  In particular, such a library would have
> symbols for TO-packaged transistors, where pins "1", "2", and "3" make
> sense (maybe with a circle around the transistor symbol, which seems
> to be more standard for PCB schematics than for VLSI schematics).  
> Such a library would also be the proper place for transformers,
> crystals, voltage regulators, and such, and MOSFETs and other mainly
> VLSI components could be moved to a different page.  What do you
> think?

That's funny because I do VLSI designs at work.  But I'm using xcircuit
for smaller-scale, smaller-budget hobby circuits where ICs and discrete
components are what I can afford to play with.  

> > Pcb's netlist reader is very picky about pin numbers and node names.
> 
> However, PCB itself seems to be very liberal about pin naming conventions.
> I will ask Harry if he thinks the netlist reader syntax can be extended to
> include arbitrary names for pins, or whether that would break stuff right
> and left.  If there's a file format standard he's following, we might have
> to go back to that to make changes.

PCB keeps trace of both pin numbers and pin names.  The names can be
anything you want, but they are just for display purposes.  Only the pin
numbers can be used to specify a netlist.  If the PCB netlist reader would
allow pin names, then calling them E B C in a pcb library would be fine.  
IMHO, better than 1,2,3, since you don't have to look up which is which.

> > Another issue that's minor but confusing is that it's possible to get two
> > Vdd nodes in the netlist.
> 
> To a point, that's intentional.  If you want a Vdd pin which gets merged
> with the rest of the Vdd network, it should be declared "Global"
> (menu "Netlist->Make Global Pin").  It's really the same problem as
> declaring the scope of a variable in software.  It prevents bad things
> from happening such as declaring a global name "E" and having it suddenly
> connect together every emitter of every bipolar transistor in your
> schematic.

Ok.  I can definitely see the point of having local names, but when you
write out a flattened netlist, if these names collide you have an illegal
netlist.  When flattening, you may need a function that turns duplicate
names into unique strings so that some other tool doesn't 1) fail to parse
the two nodes with the same name, or 2) short them together.


Regards,
Bryce