[mythtv-users] Changing channels on a new D11 directv receiver

Brian Wallen brian_wallen at hotmail.com
Fri Dec 30 12:33:35 EST 2005

Thanks so much for clearing that up.  I thought I was confused, but 
apperently I was right on track.  Thanks for all the work you've done!


>From: Jeff Simpson <jeffsimpson at alum.wpi.edu>
>Reply-To: Discussion about mythtv <mythtv-users at mythtv.org>
>To: Discussion about mythtv <mythtv-users at mythtv.org>
>Subject: Re: [mythtv-users] Changing channels on a new D11 directv receiver
>Date: Fri, 30 Dec 2005 12:13:10 -0500
>On 12/30/05, Brian Wallen <brian_wallen at hotmail.com> wrote:
> >
> > Ok, I've read the guide you wrote up on mythtv.info.  My problem is, I
> > can't
> > envision how this works.  First off, what is the difference between a 
> > modem cable and a serial cable, and when I'm looking at one, how can I
> > tell
> > which kind it is?
>The difference is that a normal serial cable goes straight through: ie the
>Rx goes to Rx, Tx goes to Tx, CTS goes to CTS, etc. They are intended to be
>used with a device that is expecting that, like a modem or an old-school
>mouse. Since these are straight-through, they are often used as extension
>cables, since you can string together as many as you like, assuming it's 
>so long that you have issues with propagation delay and signal attenuation.
>A null modem cable (or adapter) swaps the RX and TX, as well as CTS/RTS.
>This is roughly equivalent to the tin-can telephone, where the string 
>from the can at my mouth has to go to the tin can at your ear in order for
>it to work (and vice versa, the one from your mouth has to go back to my
>You can't tell by looking at it (although most null-modem cables/adapters
>will be labelled as such), but you can tell by using a voltmeter set to
>continuity and check the pins to see if they are straight-through or not.
>The easiest thing to do is just buy a cable that is what you are looking
>Secondly, where does the usb->serial adapter plug in?  The way I'm seeing 
> > now is I plug a usb cable into my receiver.  Then on the other end of 
> > cable is the usb->serial adapter.  Then on the serial side of the
> > usb->serial adapter goes a null modem cable that will plug into the 
> > port of my backend.  Is this anywhere close to being right?
>Exactly right. There are two options for this:
>1) Serial to USB: The serial port of your computer connects to a null-modem
>cable. That cable in turn connects to the USB->serial adapter, which plugs
>into the D11
>2). USB to USB: one of the USB->Serial adapters plugs into your PC, the
>other plugs into the D11. The null-modem adapter goes between the two
> > And lastly, how would I change channels using one backend and 2+ directv
> > receivers?
>you'd need two of these cables going to two different serial ports. The
>script can be modified to talk to a specific serial port or take a serial
>port as a parameter (I meant to write it that way initially, but never got
>around to it). The simplest way is to make two copies of the script
>"directv_1.pl" and "directv_2.pl" and edit each of them to hard-code the
>serial port you intend to use (/devttyS0 and /devttyS1). If you use USB,
>it's a little more complicated, as the serial ports are assigned when the
>adapter is connected, you may not be able to easily tell which is which, so
>you'll have to test it out.

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