25 Aug
2014
25 Aug
'14
4:30 p.m.
On Mon, 25 Aug 2014, David Griffith wrote:
While I'm prepping parts for P112 kits, I started
thinking about DE-9
pigtails. These things come in two different pinouts. One of them is pin-1
of the header connects to pin-1 on the DE-9. When wiring up a pigtail like
this manually, you cut the ribbon cable into two sections. One sections goes
on the top row of the DE-9. The other section goes on the bottom. The other
one has the pins interleaved. See http://661.org/p112/files/pigtail.pdf for
what I mean.
The P112 was designed with the second pinout in mind. When I bought pigtails
for my first run of P112s, I managed to get that kind. For subsequent runs, I
always got the first kind. Which pinout is more common with actual devices?
I ask this because I'm tinkering with an amateur radio project that will
eventually use DE-9 pigtails.
I've seen PCB pin headers for serial ports using three kinds of wiring. I
think whoever makes/sells these pigtails should state the wiring as
there's no single established standard. I saw two different ways with x86
PC-class computers where, reportedly at the time I had to fiddle with this
stuff (late 1990s/early 2000s), most PC equipment manufacturers used one
way but Tyan used their own (no pin assignment reference at hand, but I
presume the common one was the two-section version you've described and
the Tyan one was something exotic; they later switched to the common one
I'm told).
Yet when I got to wiring a serial port pin header on a MIPS development
board I got, none of the pigtails I had was right and I had to rewire one
(I used a DB-25 rather than DE-9 connector actually as that was what I
needed). And looking at the board schematics it was one you refer to as
"interleaved":
1->CD
2->DSR
3->RX
4->RTS
5->TX
6->CTS
7->DTR
8->RI
9->GND
10->N/C
So I think your observation is right, the two-section version is probably
more common, which is why you can get correct pigtails for it more easily.
Maciej