Re: header pin numbering

[Eric Smith <eric-no-spam-for-me@brouhaha.com>]

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?


I've never seen this one used for ordinary dual-row headers:

> 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

The only way that would be useful is if you were cabling the
dual-row header to an IDC DIP socket, in which case the numbering
would match.



This one is used sometimes:

> 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

That's how edge-card connectors are normally (but not always)
numbered, so it would be useful if you were cabling the dual-row
header to an IDC edge card socket.



This scheme is the most common:

> 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

Note that with ribbon cable, this assigns sequential numbers to
the conductors, which makes it easier to deal with alternate-ground
(or differential) signalling.