At 01:23 PM 9/5/01 -0700, Brad Velander wrote:

>         With your method, which works just fine, I find that having EBC, GDS
>or AK on the schematic is just too stupid and redundant. Who needs it?

Well, EBC etc. is explicit, whereas 1,2,3, etc. depend on additional 
context. If you have to work with other people, it is much less likely that 
an error will be made if the letters are used. Is pin 1 of a diode the 
anode or the cathode? There are two reasonable ways to think about it, and 
I have seen both.

I not uncommonly receive net lists from clients and I don't have the 
schematic. If the pins are numbered on a transistor it can be a real 
nuisance to resolve. If the pins are lettered appropriately to indicate 
function, the intention is crystal clear even if I have to mess with the 
pad names.

As to "stupid and redundant," redundancy is *intelligent.* Far fewer errors 
are made when information is redundant, because contradictions stand out. 
But if you don't want to see the letters, you can simply suppress their 
display. That's what I normally do for diodes.

Now, if it is "stupidly redundant" to display the *letters* for a 
transistor, it is only *not* redundant to display the *numbers* because the 
numbers are not explicit. In other words, to avoid redundancy, one has 
added another level of complexity, i.e., the correlation between numbers 
and pads or pad functions. The assignment of numbers to these parts is 
quite arbitrary, as many of us have discovered to our chagrin.

However, for transistors and especially for FETS, I prefer that the names 
of the pins be displayed. Sure, I know what pin is what function from the 
symbols, but I am less likely to get confused with redundant information, 
and using names or abbreviations is simple and cannot cause confusion.

Numbers are only appropriate
    (1) Where the numbering proceeds from the physical layout of the part, 
preferably according to an industry standard. And I've been bitten on this 
one more than once.... (I once laid out a DIP relay -- creating the symbol 
and footprint -- using a catalog photo of the part, and on the top of the 
relay was an explicit pinout diagram. Very nice. What I could not read on 
the catalog photo was that the diagram was a bottom view....)
    (2) Where they are arbitrary and swapping them makes no difference. As 
with a resistor.
    (3) Where using letters would make no improvement because there are no 
standard, readily recognisable names for the functions.

The majority of parts most of us use fall into category 1, i.e., DIPS and 
SOICs etc., and some early CAD systems could only handle numbers, which, I 
think, is the only reason we think that using numbers for polarized parts 
is acceptable.

Abdulrahman Lomax
Easthampton, Massachusetts USA

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