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Ask DISH: Is dual output really a hardware limitation

Discussion in 'Other HD Receiver Support Forum (811, 921, 942)' started by dishbacker, Aug 12, 2004.

  1. dishbacker

    dishbacker Godfather

    Jun 15, 2004
    I know this has been discussed time and time again, but I have to keep wondering why it doesn't work. Why is it that the SD and HD outputs can't be active at the same time?

    I have both cables hooked up to my 921 (with the SD feeding to other TVs in my house). While booting up the 921 tonight after the software download, I noticed while the silver DISH graphic was displayed on the screen, both my component and S-Video outputs were active, and even when the first blue pop-up screen displays stating that it is booting up, both outputs still work. Then, a click happens and the display appears to reset itself (i.e. similar to what happens when switching inputs on my TV from an SD input to an HD input) and the SD output goes away.

    There has been talk in the past as well of users who have connected both DVI and Component from the 921 to their TV and it worked, until they did something (I believe toggle the HD/SD button) and then only one output works.

    This all sounds to me like the hardware does have the capability to support it but the software is limiting it. Is it that the wiring within the box is capable, but the box/cpu/fan/etc itself wouldn't be able to support the multiple outputs at the same time? Does dish not want a 921 to go to multiple TVs, trying to make you get a second receiver? I also remember a electronics discussion about the firewire ports running too hot or emiting too much of some frequency (way over my programming head). Is that it?

    I'm just throwing out guesses here. In my case, I would at least like the Component Output to be active when switching the box to SD mode. Not something I do often, but it would allow me to continue to watch the 921 on my main TV while being able to send SD output to another room with the same program on.

    Just looking deeper into the technical discussion of this... not just the standard 'it don't work' reply.

  2. SimpleSimon

    SimpleSimon Hall Of Fame

    Jan 15, 2004
    Offhand, I can think of two reasons for this limitation:

    1. Having multiple outputs active may generate too much heat for the chips/heatsinks to handle - possibly due to poor thermal design.

    2. Having multiple outputs active may require too much processing power for the old, slow, obsolete CPU they put in the 921. I believe it's an 866MHz chip - that probably costs more now than a still-high-volume-production 2GHz Intel CPU.
  3. David_Levin

    David_Levin Icon/Supporter DBSTalk Gold Club

    Apr 22, 2002
    Here's what I believe is what's going on....

    The main processor is not doing the scaling - it's a separate dedicated scaler circuit (DSP chip). There's only 1 scaler in the box....

    Let's say you're watching a 1080i source and scaling it to 720p for the hd output (or just using different format modes).

    The scaler is in use and not available to also scal the 1080i to 480i for the SD output.

    Bootup is a special case.... The 921 is outputting 480p to the DVI and 480i to the SD output. Since both are the same number of lines the one scaler can handle it.
  4. SimpleSimon

    SimpleSimon Hall Of Fame

    Jan 15, 2004
    OK - I'll buy that - makes mucho sense - but doesn't explain why we can't have DVI and Component at the same time.

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