On 03:57 PM 5/09/2001 -0700, Brad Velander said:
>Abd ul-Rahman,
>         My point was only that the EBC, AK, GDS is redundant and stupid on
>the schematic because the symbols convey the function of each pin already.
>Holding only the printed schematic in your hand, the EBC, GDS and AK conveys
>what information that you didn't already know from the symbol? What does it
>tell you about where to find the Base pin on a physical device on a PCBA?
>The answer to both questions is "Nothing", right? Thus it is redundant,
>useless and clutters up your schematic with useless information.

I was going to let this one through to the keeper but nah...

1) There is no Sch clutter, the pins numbers are hidden
2) The information is not redundant, I can set a design rule that gives 
different track thicknesses to all gate connections - easily.  For instance 
- making a Pad class with all the gates is simple as in 
the  Design|Classes|Pad dialog tab I can Add a new class and add
to the non-members filter and up will come all the 'G' pins (along with the 
-GND pins).  Makes making a pad class easier.  Try that with 123-style 
numbering.  (I know this is a little contrived but the point is that with 
EBC or GDS pin numbering you can do extra filtering that is not possible 
with 123-style.)
3) Someone creating a new part knows they have to allocate EBC or GDS to 
the new footprint they are creating.  They are more likely to remember to 
the check data sheet with the alpha numbering - this has been my long term 
experience.  Since the numbering starts by default as 1,2,3 etc as you 
plonk down pads it is easy to forget to check that you have made the 
footprint correctly.  In the EBC-style the footprint is unusable until the 
alpha pin numbers are provided.  This is more likely to trigger a check of 
the data sheet.  Even if those creating footprints would normally check pin 
numbering before using a footprint, mistakes happen at 2:00 am as 
Production are banging on the door.  If the netlist load/synch chokes you 
get a healthy reminder.

>         I agree that there is no one ideal solution. With the system I use,
>I have one SOT23 footprint for a particular package size. The symbols are
>designed to match that footprint.
>         If you receive information as a netlist only, then the customer is
>responsible anyways right? They have to have used the right symbol with the
>right part. If they didn't how can you possibly tell?

Well, if a SOT-23 pin is labelled 'G' it is a fair bet that it is a 
gate.  A skilled designer has more information at their disposal to aid 
on-line grey matter DRCs as well as potentially improving the layout.  If 
it is labelled '1' then you have no method of even starting to bring high 
level interpretive skills to bear.  Even if the schematic is on your desk 
as you work, it is easy to get buried in a layout and not refer.  The pin 
number provides an extra memory jog.

Surely, Brad, you are not saying that PCB work is merely a join-the-dots 
draughting exercise?

>         Also, I don't display the pin numbers on transistors or diodes. As
>you said it would convey no more clarity because of the mixture of
>manufacturer numbering/labeling schemes. Likewise the EBC and GDS conveys no
>more information either (without the datasheet). Right? Stalemate!

Wrong, while laying out the PCB knowing that a pin is a gate rather than a 
'1', whatever that is, is certainly useful.  I have a TO-220 part.  Which 
track is the control trace and so can be thin, which are the power 
tracks.  I know easily without having to remember to refer to the Sch, do 
you?  So it does convey useful info.  The pads on the PCB are a constant 
reminder of function and will jog your memory as you work.

In many years of PCB work, EBC has never failed me.  Lloyd's is the first 
time I have seen an issue with alpha characters as pin numbers that I 
recall.  But my memory is not so good anymore and I have not used any other 
CAE package seriously for many years.

Years ago I saw many mistakes made with 123-style numbering, many of these 
were repeat mistakes.  I forced a change to the system where sch parts had 
EBC etc and the PCB parts remained at 123.  This *forced* the PCB designers 
and engineers (often one and the same) to go to databooks to check pinning 
and then manually (with careful global edits) change the PCB pads to match 
the sch and allow the netlist import to succeed.  This was a fairly drastic 
measure but it broke the cycle and made the engineers and 
techs  sufficiently aware of the problem that it hasn't been such an issue 
recently.  More recently we have been using PCB footprints that are fairly 
specific.  So, for instance, we have a BC8XXREFLOW  footprint, which has E, 
B, C pad numbers.  A designer is welcome to use this footprint for any part 
as long as they have checked that it does indeed conform to the pin 
functions of the BC846, BC856 etc series parts.  But if they use it 
incorrectly then they are hung over the balcony while the vultures peck 
their eyes.  Coz they knew better and were just being lazy.

We use EBC-style numbering mainly as some protection against human failings.

Bye for now,
Ian Wilson

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