Re: header pin numbering

[mjmahon@aol.com (Michael J. Mahon)]

In article <3E5AEAD9.4000807@telus.spamless.net>, Wayne Stewart
<waynes@telus.spamless.net> writes:

>I’ve seen boards with 40 pin headers like the one on the
>TransWarpGS marked on the board with any of these numbering
>schemes. Any opinions as to which is preferable in this case?
>
>
>20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1
>
>21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

This is standard DIP-package IC pin numbering.

>
>
>
>20 19 18 17 16 15 14 13 12 11 10 9  8  7  6  5  4  3  2  1
>
>40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21

This is the way many 2-row pin-and-socket connectors order pins.

>
>
>
>39 37 35 33 31 29 27 25 23 21 19 17 15 13 11  9  7  5  3  1
>
>40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10  8  6  4  2

This is standard IDC connector ordering, derived from the ordering
of the wires in the flat cable.

If you have a cable with two different _kinds_ of connectors on each
end, then something has to give.  ;-)  You can pick the most "significant"
ordering and force it on the cable and the other connector, or you can
keep each connector with its "natural" order, and then force someone
reading the schematic/PC board to "decode" one scheme into another.

I prefer the first approach for my own sanity, but I find that the second
approach--with wires numbered differently on different ends of a cable--to
be quite common.  (Perhaps the reason is that connectors and standard
layout templates usually have standard pin numbers on them, without
regard to what they connect to, of course.)

-michael

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