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

[Bruce Markey]

Ray Olszewski wrote:
...
> If neither of these ideas pans out, I'm left with suggesting you look 
> for one of those old RS232 troublshooting boxes, that had red and green 
> LEDs to detect which pins were active. (I don't know where to find these 
> today; mine is probably 10 years old.)

If you're in the Bay Area, try Halted Specialists (HSC) at
Lawrence and Central or, of course, Weird Stuff Warehouse.

> Good luck. I'd like to see this procedure get well documented.
> 
> At 11:30 PM 6/9/2003 -0400, John Klimek wrote:
> 
>> Ok, here are my findings so far.
>>
>> DB9F pin assignment is definitely as follows:
>> 5 4 3 2 1
>>  9 8 7 6
>>
>> RJ22 pin assignment seems to (definitely?) follow:  (when looking at the
>> bottom, pin-side)
>> Pin-1
>> Pin-2
>> Pin-3
>> Pin-4
>>
>> Following the pin assignment, I've connected:
>> (RJ22-to-DB9F)
>> 1 - to - 5  [ground]
>> 2 - to - 2  [receive]
>> 4 - to - 3  [transmit]
>>
>> Here is what happens:
>>
>> 1)  If I DO NOT connect the RECEIVE line (2 - to - 2), I can transmit 
>> to the
>> receiver PERFECTLY.  The receive changes channels, etc, etc and works
>> perfectly fine.  Of course I still get "a Timeout" response from the 
>> receive
>> because the RxD line is not connected.  However it will still change
>> channels.
>>
>> 2)  If I DO NOT connect BOTH the RECEIVE and the GROUND line, whenever I
>> transmit to the receive it will change to WEIRD channels and do weird
>> things.
>>
>> 3)  If I connect ALL THE WIRES, as soon as I plug the cable into the
>> computer and the receive, my satellite receiver will turn itself on 
>> and off
>> constantly.
>>
>> I believe my problem is DEFINITELY located in the receive line.

Well, this may sound dumb and simplistic, but here goes.

Maybe you should only connect TX and GND. If you think
of the data port as a substitute for an IR device,
there should be no out bound data from the cable box.
If, as you say, you can change channels, that may be all
you need.

If pin two had random noise, that may cause the serial port
on the Linux box to do weird things like re-negotiate baud
rate, send HUPs, long breaks or whatever. Try connecting
just the two pins and set the terminal parameters to assume
that the port is connected even though there are no signals
on RX. No HUP, no flow control, etc.

--  bjm