At 09:46 AM 10/4/2002 +1000, Hugh Stevenson wrote:
>I am suffereng from a problem that when I place schematic symbols the
>Designator and Part Type text is on a 5 grid when my grid is (and always
>has been ) set to 10.  It only happens sometimes.  Does anyone know the
>secret to avaoiding it?

The position of designator (and other enabled) text is automatically 
determined by Protel for initial placement. Sometimes the position is 
inherited from another symbol, but that would beg the question.

I have not investigated the cause, but, as was Mr. Wilson, I am familiar 
with the issue, though I have not compared designator location with symbol 
extents.

Symbol extents (the maximum and minimum X,Y coordinate for all primitives 
in the component) may or may not include the width of the outside 
primitives. However, the center of extents, regardless, can easily be on 
the half grid if the width of the outside primitives is irrelevant or is, 
say the grid size, or if primitive width is irrelevant. Primitive width 
*is* relevant with PCB, but it might not be with Schematic.

So if features or full extent are on a 10 mil grid, and default line width 
is 10 mils, the calculated position of the midpoint will be on a 10 mil 
grid with the full width is an even multiple of 10 mils, and on a 5 mil 
grid if the full width is an odd multiple of 10 mils.

Because symbols might even be designed on a 1 mil grid, or they might have 
features with full extents not on a 10 mil grid, the calculated midpoint 
may be on any grid, it will not be restricted to 5 or 10 mils.


Abd ul-Rahman Lomax
LOMAX DESIGN ASSOCIATES
PCB design, consulting, and training
Protel EDA license resales
Easthampton, Massachusetts, USA
(413) 527-3881, efax (419) 730-4777
www.lomaxdesign.com



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