At 09:19 PM 2/5/2002 +0000, Steve Wiseman wrote:
> > Elsewhere I described an alternate method of doing a virtual short, that
> > is, a jumper footprint that appears as open to DRC but is actually shorted
> > in plot. This alternative involves placing a track, as part of the VS
> > footprint, on an otherwise unused mech layer.
>I used to do this, and still do sometimes for jumper links. However, it's
>extra steps at photoplot time, and extra steps = extra opportunities for
>mistakes. Since, by the time a board this complex goes out, I've normally
>been working 20-hour days for a week, the simpler I can make things, the
>longer the PCB shop will let me sleep before phoning for clarification :)

It is one extra step, which does not need to be repeated. This is one great 
feature of the CAM Manager: you can set up individual parameters for each 
plot if you want, and then all [enabled] plots will be generated at once. 
Usually we don't need to do this, but making such a shunt is a case. I also 
use this feature to generate formal drawings, merging a different mech 
layer. Remember, if you *do* forget to short the part, it is not a big 
disaster, if you have made the parts properly. You might even do both: a 
virtual short and a shunt. That is, take your current virtual shorts and 
add mech layer track to short them.

If we had layer associations it would help. (Top is associated with Top 
Overlay, so when you flip the board, the overlay flips with it. That 
doesn't happen with the mech layers, which is a Protel deficiency. Tango 
DOS had top and bottom assembly layers in addition to the legend layers, 
they flipped with the part....)

Thus one should make a top layer shunt and a bottom layer shunt, and they 
should not be flipped in design.

Protel should, in general, fix the photoplot routines so that WYSIWYG, 
without *any* deviation except the unavoidable one of roundoff error. There 
is little reason for aperture matching in times when the plotters can 
handle D-codes to D999. I'd make aperture matching an option that defaults 
to zero. *Maybe* I would accept minimum aperture matches that represent 
only the minimum difference resulting from unit shifts (mm-mil). But I 
think not.

By the way, it's pretty obvious why the rotated pads did not plot. The plot 
routine quite properly does not draw pads or any other primitive with a 
zero aperture unless zero is the actual size of the primitive. The 
programmer trapped it out, it would lead to lockup.

Abdulrahman Lomax
Easthampton, Massachusetts USA

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