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Ntsc -> vga — Parallax Forums

Ntsc -> vga

Paul BakerPaul Baker Posts: 6,351
edited 2009-01-15 03:37 in General Discussion
Is anyone aware of a chip which converts NTSC to VGA? I thought I'd ask the community before beginning my search.

TIA

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Paul Baker

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2009-01-08 20:43
    Paul,

    I haven't seen a single chip solution, only a chipset solution that was used. Mainly (I think) because of the differences in refresh and other timing. The NTSC needs to be interpreted/dithered into a format compatible to VGA and then stored in some kind of dual port memory at one rate. The memory can then be read at another rate compatible to VGA... most likely 640x480 ... much larger and you have very noticeable pixilation on the VGA.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2009-01-08 21:00
    Thanks Beau, do you remember what chipset it was? I'm mainly looking for the decoding the NTSC to the consituent RGB values (I can handle the retiming to VGA), reinventing the wheel will likely break the budget compared to a pre-rolled ASIC chip.

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    Paul Baker
  • uxoriousuxorious Posts: 126
    edited 2009-01-08 21:05
    A friend recently had the same desire and ended up buying one of these from Amazon for his project and pulled it out of the retail housing and installed as a PCB in his chassis.

    http://www.avermedia.com/avertv/Product/ProductDetail.aspx?Id=164&device=3

    http://www.amazon.com/AverMedia-MTVDVIBX7-Avertv-Dvi-Box/dp/B001DVVJYG/ref=sr_1_3?ie=UTF8&s=electronics&qid=1231448655&sr=1-3

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    ~~ dRu ~~
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2009-01-08 21:10
    Paul,

    I don't remember off hand, I can check later.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • Paul BakerPaul Baker Posts: 6,351
    edited 2009-01-10 00:45
    Thanks for the links dRu, but this is for a commerical application.

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    Paul Baker
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-01-10 01:01
    Paul,

    Here is an article that explains how one person did it. It uses a line buffer (as opposed to a frame buffer) and a lot of MSI and discrete components, but the same principle could be applied to a more modern design. A Propeller could probably sponge up a lot of the parts. Without reading the article closely, I don't know how he addresses interlacing without buffering an entire frame. 'Seems like it would flicker a lot.

    -Phil

    Post Edited (Phil Pilgrim (PhiPi)) : 1/10/2009 1:07:25 AM GMT
  • Paul BakerPaul Baker Posts: 6,351
    edited 2009-01-10 03:33
    I couldn't find the V7021 he claims to use, but a quick search of Digikey yeilds useful results, AD and TI make chips that decode NTSC/PAL/SECAM, though they aren't cheap.

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    Paul Baker
  • LeonLeon Posts: 7,620
    edited 2009-01-10 23:14
    I'd use the ADI ADV7184. I've got a Blackfin kit with the earlier ADV7183 on it, IIRC. You'll also need something like a Blackfin and some RAM to go with it, of course.

    Leon

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    Post Edited (Leon) : 1/10/2009 11:20:49 PM GMT
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2009-01-11 05:33
    Phil Pilgrim,

    The link that you posted uses the same technique that I was remembering. If the video speeds weren’t so different it wouldn't be so complex. If you had a custom VGA monitor that matched the same NTSC/PAL resolution (see below) , you might be able to reduce some of the complexity, but then there is still the matter of splitting the NTSC/PAL to RGB.

    NTSC resolution standards:
    · NTSC (resolution 648 x 486 - preferred format)
    · D-1 NTSC (resolution 720 x 486)
    · D-1 NTSC Square Pix (resolution 720 x 540)

    PAL resolution standards:
    · PAL (resolution 720 x 486)
    · D-1 PAL (resolution 720 x 576)
    · D-1 PAL Square Pix (resolution 768 x 576)

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-01-11 06:00
    Beau,

    What I can't figure out, though, is that for each field, each line is buffered and sent twice (back-to-back, starting one line later) to the VGA, which would work fine for non-interlaced video. But for interlaced video, the VGA would display even fields and odd fields alternating at a 60Hz rate:

    00000000000000000000 11111111111111111111
    00000000000000000000 11111111111111111111
    22222222222222222222 33333333333333333333
    22222222222222222222 33333333333333333333
    44444444444444444444 55555555555555555555
    44444444444444444444 55555555555555555555
    66666666666666666666 77777777777777777777
    66666666666666666666 77777777777777777777

    instead of being interlaced:

    00000000000000000000 00000000000000000000
    11111111111111111111 11111111111111111111
    22222222222222222222 22222222222222222222
    33333333333333333333 33333333333333333333
    44444444444444444444 44444444444444444444
    55555555555555555555 55555555555555555555
    66666666666666666666 66666666666666666666
    77777777777777777777 77777777777777777777

    The resulting 30Hz flicker would be very uncomfortable to watch. It seems that for a proper display of interlaced NTSC, an entire field would have to be buffered to play back, interspersed with its complement, as the complement was being received.

    -Phil
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2009-01-11 07:21
    Phil Pilgrim,

    I didn't look at the circuit in too much detail, but perhaps there is a trick here, or the NTSC is just being converted using only half the field.

    Here is a good description of how the video is interlaced... even a half field view example.
    nickyguides.digital-digest.com/interlace.htm

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • uxoriousuxorious Posts: 126
    edited 2009-01-12 18:51
    My apologies for missing the commercial solution aspect. In that case, the only suggestion I have is a little overkill. Phillips (now NXP) makes a media processor that when partnered with the proper TV codec would be a solution. However, the setup is also capable of converting HD, decoding DVD, MP3, etc, and a myriad of other items that make it a single chip solution for high end media products. The product was a very high end CD player and the board controlled all of the CD reading (bit perfect lossless reading), flash memory, 7" display, an SD card, ethernet, USB, SPDIF, etc.

    NXP Nexperia Media Processor PNX1502E

    In the Phillips "low-BOM Media Player Reference Design" they use a Philips SAA7109A TV Codec in a 156 ball BGA package.
    "encodes up to 800 x 600 resolution PAL or NTSC; decodes PAL, NTSC, SECAM and High Definition 720p and 1080i TV output"

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    ~~ dRu ~~
  • Cluso99Cluso99 Posts: 18,069
    edited 2009-01-15 03:37
    If you just used a window (NTSC 648x486) within a VGA display of 800x600, with the remaining pixels always black, this would be much easier to do and may be able to be done within a prop. Certainly, the VGA display object could generate the output. Just a thought?

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