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embedded video?

Discussion in 'Electronic Design' started by Bob Stephens, Jan 14, 2004.

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  1. Bob Stephens

    Bob Stephens Guest

    I need to generate simple NTSC composite video text as a last minute
    feature on an 8051 based embedded project. I have found some software
    examples but they really chew up CPU time. Does anyone know of a one chip
    solution for generating black and white video? I'm picturing something like
    a "video UART" which you could spit ascii characters at and let it generate
    the composite video, sync etc. I'm probably dreaming.


  2. Maybe look for OSD (on-screen display) devices.

  3. CBFalconer

    CBFalconer Guest

    No you're not (dreaming). They used to exist. Whether they still
    do is another matter. Look for things to handle menus on TV
    screens, etc.
  4. We can get close, with a VGA-232 product, but unfortunately this
    outputs PC-VGA video, not NTSC. (ie plugs into a std VGA monitor)
    PAL/NTSC give poorer text quality, but do have a place where you need
    to overlay (character insert) text onto pictures. In this case, you need
    to genlock the character generator to the picture sync.
  5. Bob Stephens

    Bob Stephens Guest

    Well, it gets worse. When I said NTSC I was actually fudging a bit. I need
    to generate non standard RS 170 with a sync pulse amplitude of 0.75 V +/-
    0.25V and a 3.0V peak video signal.

  6. Bob Stephens

    Bob Stephens Guest

    Yes, I've downloaded a couple examples - may end up going that route.

  7. Bob Stephens

    Bob Stephens Guest

    Unfortunately, not an option. This thing is talking to a primary flight
    display in a glass cockpit airplane.

  8. Luhan Monat

    Luhan Monat Guest

    Build a video generator out of a PIC (they're cheap) and feed it
    parallel data. I've seen seveal listings of how to make NTSC character

    Viola! Now you have a cheap video character ic!
  9. Luhan Monat

    Luhan Monat Guest

    Also, if you really want to feed it serial, use a PIC16F628 with a
    hardware UART built in. You should be able to read incomming data
    without losing the NTSC timing.

    Another option is to generate Closed Caption signals in the VBI interval
    (I've done this). Then just set the TV to show closed captioning. You
    dont need to generate NTSC here, just locate the proper VBI line and jam
    the codes onto it. Text-over-video, the easy way!
  10. Ben Bradley

    Ben Bradley Guest

    In, Bob Stephens

    What about adding another 8051 to run the video code, and using
    serial comm from the original 8051?

    And while I'm at it, did you explain the costs of "last minute
    features"? OTOH, it could be argued that it's our jobs to pull off
    these things.

    I hesistate to mention this because 1. it's probably not made nor
    really useful anymore and 2. it shows my age. :) But... there was the
    ubiquitous Motorola 6845 "CRT Controller" chip. I forget how many
    products this was used in, but I recall it on the original IBM PC
    color card, and probably the IBM PC mono card and original Herculese
    mono/graphics card. The Apple ][ used its own TTL DRAM refresh
    circuitry to also do video output of RAM, but there was an 80-column
    card for the ][ that used the 6845.
    That may not be a problem - many things generate the composite
    video signal by using summing resistors on digital port outputs, and
    you should be able to change the levels by changing resistor values.
  11. Bob Stephens

    Bob Stephens Guest

    I'm considering using a low end PIC - mainly because I have source for a
    couple of examples in assembler and don't have time to port them to 8051.
    Another problem is that we are running out of real estate on the PCB.
    Yup. That's about the size of it. Fortunately these last few features -
    video generation, GPS receiver, Fibre Optic transceivers, MIL 1553
    communication, USB 2.0 are all considered trivial by the boss ;)

    Probably a large-ish through hole device yes? I'll check on it though.
    Thanks Ben
  12. Google SAA5246A_CNV_3.pdf
    i2c bus interface, will genlock and add your text 25 lines of 40 chars, color.
    can run standalone (PLL mode off), 5V, 27 MHz xtal..
    If you need drivers see
    for some GPL C code.
  13. Quack

    Quack Guest

    You could try the BOB-II, which is a small board (30-pin SIMM) which
    can be controlled via serial commands from your uC.

    I used one once for video overlay, very easy.
    I think its capable of 80x40 ascii or something like that, and cost
    about $80 as i recall.

    It was very quick and easy to start using, just power, serial line and
    video out if you dont want to overlay.\products\specs\Video Overlay Board.htm

  14. Bob Stephens

    Bob Stephens Guest

    I saw their website. Actually the BOB II is "not recommended for new
    designs" it has been supplanted by the BOB III. Unfortunately I need a
    surface mount solution.

  15. See

    Never used them myself. Maybe too expensive for what you are looking for?

    Use a Faster 8051?

    Thanks, VIncent
  16. Philips has an 8051 with OSD on board specifically for monitors. but
    possible it genlocks on the RGB signal.
    ST also makes this

    another option is to code on in a differnt 8051.
    Check out the 8051 make by CYGNAL. www.cygnal. they have some variants that
    run 100 mips ! i use these frequently.

    I had plans of making a similar device to what you need
    use a LM1881 as sync separator.
    That way you get Horizondal and vertical sync.
    Hook these two into INT0 and INT0

    I use the built in ram to make a pixel map ( the cygnal has a lot of ram up
    to 8192 Kbyte ) So you could even create 'pages'

    Vertical sync resets my 2 'scan' counters.
    using timer 0 i increment one of the conters that scans the pixelmap
    When Horizontal sync happens the line counter increments and the pixel
    counter is reset.

    The pixeldata is avaialble on port pin. it controls controls an 4066 analog
    switch that interrupts the incoming vieo , and second 4066 switch toggles
    between balck and white levels ( preset with stupid resistors.
    That way i can overlay textlines where i want. since i use a pixelmap i van
    even make drawings.

    My signals are thus synced with incoming video and 'ride' on the existing

    This was the idea. i did some calculations and using a 25 mhz clocked
    Cygnal i could do a 20 charakter a line 8 line display without problems.
    ( 128 pixels by 64 pixel equivalent of an LCD graphic display )

    I never built it though.
  17. William

    William Guest

    I think you're a good 15 years too late. The proliferation of the PC
    and the many video cards used in it has pretty much destroyed the
    market for the old character generator chips. If I were to need such a
    part today, I would probably grab an FPGA and start coding. Depending
    on your needs, it could be a pretty small block, perhaps to fit one of
    the less expensice CPLD parts from Cypress, for example.

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