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Apple 30" Full Rez using single-link DVI?

Discussion in 'Macintosh Computers' started by wjchan, Aug 25, 2004.

  1. macrumors newbie

    Do you think the 30" will accept a lower refresh rate and run full rez using single-link? With 165MHz of bandwidth, single-link DVI should be able to drive it at up to 40Hz. Just wondering.

    BTW, the spec indicates that it'll run at lower resolutions (probaly using single-link): 2048x1200, 1920x1200, 1280x800, 1024x640.
  2. macrumors G5

    Sun Baked

  3. macrumors 6502


    At the WWDC (at least I think) Jobs showed that the 30" cinema displays require 2 DVI connections--1 for each half of the screen. The way I'm looking at it (I could be wrong) it appears that one DVI runs the bottom half and 1 runs the top half.

    In short, I don't think so.
  4. macrumors 65816



    You are misinformed. Dual Link DVI is a special KIND of DVI connector. The 6800 has TWO DLDVI connectors that drive TWO 30 inch displays. This is a very common misconception that about 75% of people have about the new display.

    As for the original poster... this is an LCD monitor...

    Why are you talking about Hz refresh rates? LCDs don't operate on that... it's MS response time, and you MUST have the Dual Link DVI to operate the monitor.
  5. macrumors 68030


    IIRC there's something called the blanking interval that appears to be somewhat similar to the refresh rate on a CRT. Apparently the 23" LCD increases it slightly to run at 1920x1200.
  6. macrumors newbie

    Hey man, I have been using the latest and highest res LCD monitors since the IBM T210 and T221 so I think I know a few things about high res LCDs. The T210 is a 2048x1536@60Hz LCD which is beyond the bandwidth limit of single-link DVI. I've been creating custom timing files on the PC and using switchResX on the Mac side to drive it at 30Hz to 48Hz. My current desktop setup is a pari of IBM T221s--one at 25Hz and another at 48Hz.

    There's nothing magical about LCDs. Your graphics card is still continously REFRESHING the data over DVI.

    And how do you know dual-link is REQUIRED?
  7. macrumors 65816



    Yes but the blanking interval refers to the refresh on the entire picture... If I'm not mistaken, LCD blanking intervals are per-pixel only, which is why there is no full image refresh time... but rather ms response time.
  8. macrumors newbie

    Blanking interval refers to the non-picture data that monitors (CRT/LCD) need in order to sync up to the data. In the case of CRTs, the blanking interval is also needed in order to wait for the beams to move to the right position (bottom back to top, e.g.). Since LCDs don't have a beam scanning, the blanking interval can be reduced to fit more data in. Hence the term reduced blanking interval for driving high res LCD.
  9. macrumors 65816



    I could be wrong about refresh rates on LCDs, but I was always under the impression that the blanking interval was referring to the LCD response to image data being sent to the monitor.

    As for dual-link, it's because all 24 pins are being utilized on the DVI connector. Sure, the monitor will fit but it won't be able to display all the pixels.
  10. macrumors 65816



    Ah, thanks, that clarifies things.
  11. macrumors newbie

    LCD driver chips mimic CRTs to certain extent. Single-link DVI has a max bandwidth of 165MHz according to DVI 1.0 spec (Silicon Image makes some xmiters and rcvrs that go up to 220MHz but that's another story.) As long as your (Width x Height x Refresh) + Blanking Interval is below 165MHz, it is within specification. Whether the LCD driver chip will *accept* the particular resolution and refresh rate is a different matter.

    Dual-link DVI has another set of data channel (3 extra pairs or 6 pins because of the differential nature.) In a dual-link setup, the even pixels travels in 1 channel (6 pins) and the odd pixels in the other (another 6 pins). This effectively doubles the maximum bandwidth to 330MHz.

    I guess I'm tightening up and simplying my question to: Will the Apple 30" LCD interface chip accept 2560x1600@ around 30 to 40Hz over single-link?

    I should have the answer soon after 9/17 if the Apple's order-entry system is correct. In the mean time I'm just thinking out loud.
  12. macrumors 68030


    Its either yes or no. The LCD that Apple puts in their displays might not accept 30-40hz refresh rates... thats pretty low even for an LCD (only 60% of the normal 65hz thats LCDs use).
  13. macrumors 6502a

    30/40 hz... hmmm and YOU want to wath anything at such a low rate????? headaches and more... here we come ;-) if it would be even possible in the first place!!
  14. macrumors newbie

    Maybe there's a confusion over terminology so I'll call it computer->LCD update rate. Unlike CRT where the image formed on the phospor decays very quickly, the TFT LCD panel retains the image until it's updated. So even at low update/refresh rate, there's no flickering. But the catch is that at below 30Hz update/refresh rate, the human brain can detect the lag in response time (from the time you move the mouse to the pointer actually moving, for example.) 60Hz is a nice update rate but anything 30Hz+ is acceptable.
  15. macrumors 68030


    oh, do post your desktop in theaugust desktops forum. pretty pleeeeeze? at full rez o' course
  16. macrumors 6502a

    psycho bob

    I don't see what all the confusion is about. The 30 inch requires all the pins to be connected that the DVI standard supports in order to effectively supply enough data, the only card that meets that requirment is the 6800. It isn't a question of whether it will work at a lower resolution/frequency on a different card. The best that will happen is you will see half the data. Steve said so at WWDC and if you read the few (limited) details apple have released they say the same thing.
  17. macrumors newbie

    Depends on the LCD interface chip LG/Apple is using. The T221 can do 3840x2400@13Hz over single-link DVI. Like I said above, dual-link splits even and odd pixels onto 2 different channels. You won't get half a screen if 1 link is missing. The DVI 1.0 spec dictates that dual-link devices have to speak single-link also. The question boils down to whether the LCD interface chip will accept 2560x1600 over single-link. I'll have the answer end of next month. It'd be nice if it did because of the huge installed base of single-link DVI cards out there. And like I said above, update/refresh rate over 30Hz is quite acceptable.
  18. macrumors 6502a


    TVs run at 30FPS (well its actually 60 but it plays each frame twice to reduce flicker on CRT based TVs) so a video should look good.
  19. macrumors newbie

    I've posted my Winblows 7680x2400 desktop. As soon as my friend's 30" shows up, We'll be doing a side-by-side IBM T221 and Apple 30" under OS X. Should be fun comparing the same window at 204dpi and 100dpi. The resolution-independent stuff should come in handy!
  20. macrumors G4

    Speculation aside, this link cannot be clearer. The 30" Cinema Display requires the NVIDIA GeForce 6800 Ultra DDL card. You do not have the option of using a single-link DVI with Apple's monster LCD monitor.
  21. macrumors newbie

    It's called marketing. The IBM T221 supposedly requires IBM Intellistation to drive it. Right...

    Maybe you won't get plug-and-play with single-link. I'll be trying SwitchResX at 2560x1600@30 to 40Hz with single-link. I'll probably try a Quadro FX 3000 on the PC side with DL and SL.

    Your blanket statement is just wrong. The resolutions below 2560x1600--even at 60Hz--certainly fit within the 165MHz bandwidth of single-link. And like I said, the DVI 1.0 spec requires dual-link DVI devices to speak single-link also.
  22. macrumors G3


    Well, since you seem to know all the answers... why did you ask? :confused:
  23. Moderator emeritus



    What do you do that you need a 7680x2400 desktop? :eek:

    Very cool :cool:
  24. macrumors G4

    First off, the Apple 30" Cinema Display is not an IBM monitor. The IBM Intellistation is not a graphics card, it is a computer. My reading of this web page tells me that the big Apple display at 2560 x 1600 significantly exceeds the 2048 x 1538 standard maximum resolution at 60 Hz of dual-link DVI. Contrary to your statement, single-link DVI tops out at 1920 x 1080 @ 60 Hz. I infer that Apple and NVIDIA are pushing the envelope. Unless you can present documentation to support your speculation, that's all it is--uninformed speculation.
  25. macrumors newbie

    Dude, it's been covered. Read this thread again. Here's a quick summary: single-link is limited to 165MHz pixel clock (resolution x refresh + blanking intervals); most high res LCDs can be driven beyond your faux limit of 1920x1080 by lowering the refresh/update rate; LCD retains image so there's no flickering at low refresh/update rate.

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