Date   : Sat, 16 Sep 2006 11:07:42 +0100
From   : Philip Pemberton <philpem@...>
Subject: Re: AMX mouse wiring

Bob Devries wrote:
> More info on my mouse problem:
> I swapped the two VIA chips, and found no difference.
> The BBC in question has a Revision 4 motherboard. It is fitted with the 
> 8271 floppy disc controller, and the speech chips, but no econet.
> I hope I have the correct pinout for the user port Pin 1 is at the east 
> side and the pins number 1 to 10 along the north edge, and then 11 to 20 
> starting at the pin 1 end again. If this is not correct, please let me 
> know.

That pin numbering scheme is completely wrong.
IDC connectors are numbered like this:

   1 3 5 7 9 11 .... 19
          +---+
+--------+   +--------+
| o o o o o o o o o o |
| o o o o o o o o o o |
+---------------------+
   2 4 6 8 10 ...... 20

The little arrow on the connector denotes pin one -- normally the red line on 
the cable. If you pull the back off the connector (assuming you've got an 
uncrimped one), you'll notice that the pins are interleaved. Near the arrow, 
there will be one pin that's closest to the outside of the plastic - that's 
the IDC tag for pin one. Pin two is the one below it, about 0.05" (1.27mm) to 
the right. Pin three is then on the same row as pin one, 0.05" further along 
than pin two. This continues to the edge of the connector.

Thanks.
-- 
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