Re: gEDA: Has anyone done a symbol for an Atmel AVR?

[lash-at-NOSPAMtellabs_dot_com]

> 
> Ales Hvezda wrote:
> > 
> > Hi,
> > 
> > >
> > >Has anyone already done a symbol for the Atmel AT90S8515?
> > >
> > >If not, I'll probably give it a shot over the next few days.
> > 
> >         I haven't run across any Atmel symbols.
> > 
> >         If you have any questions, let me know.
> > 
> >                                                                 -Ales
> 
> IIRC, the 90S8515 was designed to have the same pinout as an 8051 so it
> could
> be used as a pin-compatible replacement, so you might start with that.
> 

Yes, it is VERY similar.  I stumbled into this discovery while looking
for a symbol to use as a model, and luckily I grabbed the 8031 first,
and realized I didnt need to change much.  Thanks for mentioning it.

I do have a sort of "style" question.  The 90S8515 (and the 8051 for
that matter) have a lot of pins that can be used as either I/O ports or
some other special purpose.  For example, if you are not using external
memory, the address and data busses can be used as general purpose
I/O ports.  For the design that I am doing, (actually copying, I am
just trying to get a feel for the tools by copying a simple design,
generating a netlist for PCB, and laying out a simple board), most 
of the pins are being used for general purpose I/O.

When creating the symbol, would it be better to have both functions
of a pin listed, or only one, and if only one, which one.  For example
I started modifying the 8031 symbol, and I decided to list both so I
had something that looked sort of like

   1 |
  ---| PB0 (T0)
     |
   2 |
  ---| PB1 (T1)


etc.  Which is  fine, except that you need to widen the symbol some
to get all of the special purpose pin names in there.  Also, there
is the question about what to do when the the pin can be either a
port pin or an inverting input or output.  In that case should you
include a bubble or not?  For example, there is PD6 which is also
/WR.

I suppose this might be an argument for having multiple symbols
for the same device, but it seems you could go crazy and create
too many devices.

Is there a general policy about this?  I didn't find it in
a quick read of the "Component Symbol Guide".  My own preference
would be to have both functions listed for most of the pins,
mainly for debugging purposes.  If you see a signal acting
strangely, and you look at the schematic and see that the
special function would make it act that way, it might save
a bit of time.

Bill