[mythtv-users] DirecTV (RS232-to-RJ11 cable) -- I think I figured out my problem!

Ray Olszewski ray at comarre.com
Mon Jun 9 18:06:25 EDT 2003


At 04:50 PM 6/9/2003 -0400, John Klimek wrote:
>I built myself a DB9-to-RJ11 cable and have been having some problems.
>
>On the BACK of my DB9 connector, it appears to last the pin numbers as
>follows:
>
>5 4 3 2 1
>  9 8 7 6
>
>However, when I searched for RS232 pin assignment, I found the following:
>
>1 2 3 4 5
>  6 7 8 9

There is no one correct answer, since male and female connectors are mirror 
images (and of course, the wiring side of a DE-9 is the mirror image of the 
pin side ... I don't know which of these you are calling the "BACK" of the 
connector or which side you are describing the pinouts with respect to). 
This URL -- http://www.rhinorobotics.com/stwire9-25.html -- gives both sets 
of pinouts ... viewed, as is so customary that they don't bother to say it, 
from the pinout side, NOT the wiring side, of the connector.

Assuming a standard serial port at the PC end, it requires a female 
connector on the cable, so the correct pinouts are the first of the two you 
list above.

>However, my cable SOMEWHAT worked.  It was able to change channels, but it
>didn't receive a "Success" signal after sending the command.

One interpretation of this is that you have TX wired correctly but not RX. 
Since TX is pin 3, it goes to the same pin with either of your pinout 
choices, but RX, pin 2, changes. In this case, you would also have SG 
miswired ... I've seen odder things than a serial cable without a ground 
return working, but that might cause some, as you say, "very weird results" 
... especially since I don't recall what handshaking line, if any, this 
cable uses.


>I rewired my cable (using incorrect (?)) using a 50" (might be longer)
>cable, and I'm getting very weird results:

I assume you mean to write 50' (50 feet), not 50" (50 inches).

50 feet is long, but not unreasonably long for a standard serial cable. 
Back in the days when I used a lot of serial connections, I used cables up 
to 100 feet routinely (to connect serial terminals to multiuser PCs ... I 
*said* it as a long time ago). Of course, what is generally true may not be 
true in a specific instance, so you might want to check on whether the 
DirecTV device has some wimpier serial implementation than the standard.

>1)  When plugged into one computer, the satellite receiver kept turning on
>and off every few seconds.
>2)  When plugged into the other (Win XP, using DTVCON), it somewhat worked.
>It would change channels, but sometimes it would change to the wrong channel
>(is my cable too long?)  and I was still unable to receiver a "Success"
>response from the satellite.  I got a ton of Buffer errors.
>
>Sorry for the long post.
>
>I'm wondering if a 50" or 75" cable is too long for the cable and is my
>wiring incorrect?

Probably not too long. But if you are worried about this, test with a short 
cable (cables aren't that hard to make if you know how, as you clearly do).

You don't actually *say* how you wired the cable, so I can't say whether 
what you did is right.

>I'm using a continuity tester to make sure the signal is passing through the
>cable, so I know that isn't the problem.
>
>Thanks for any help.  After I get my cable working complete, I'm going to
>write a very detailed HOW-TO with pictures to help out anybody else who
>might be having problems.

If you are the guy who posted on this a week or so ago, I **think** I 
recall two things:

1. The DirecTV end was an RJ22, not an RJ11.

2. The Web sites about wiring this cable have at least 2, maybe 3, 
suggested wirings. If you have RX, TX, and SG all wired correctly, but 
whatever handshaking line the DirecTV device expects to use is wrong, that 
could cause intermittent errors.

(If you post again, please include a URL for the cable-wiring diagram you 
actually followed.)





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