Connect with us

BT601 / 656 PAL Video Buffer Size

Discussion in 'Electronic Design' started by Joe G \(Home\), Jul 29, 2006.

Scroll to continue with content
  1. Hi All,

    I wanted to calcuate the dual port ram buffer size for the following PAL
    video in BT601 / 656 digital format.

    625 lines per Frame, sampling at 13.5MHz and assumeing 864 samples per

    Is the buffer size 625 x 864 = 540,000 bytes?... Is this std for PAL

    Can you recommend any video forums or news groups?

    Thanks in Advance

  2. can you just get away with using the active samples?
    Active video resolutions are either 720x486 (525/60videosystems)
    or720x576 (625/50videosystems).

  3. Oh Yes,

    Data outside the 720x576 is fixed and known, and doesn't need sampled.


  4. As other have said, you don't need to sample the line and frame retrace
    but you need to double the memory if you want the color. There are 2
    13.5MHz streams, 1 for luma and the other multiplexed for
    half-bandwidth R-Y and B-Y channels.

  5. Just remembered, 656 serial stuff is 10 bit, if you use just 8bit you
    save some memory, and 8 bit was good enough for "broadcast quality"
    for years

  6. Thanks Martin and Glenn,

    My goal is to use a micro (connected to a SD card or larger serial flash
    mem) connected to a Averlogic dual port frame buffer (AL440) to drive a
    Philips SAA7128 / SAA7120 (composite video out).

    The AL440 has an 8bit sequential in and out ports that can be clocked from
    the SAA7120 / SAA7128.

    I am just trying to guage the memory size of the flash and AL440 for one
    complete frame.

    I have access to these parts from Averlogic, Philips, and SST ... so I would
    like to use these.

    I think I will need the to include the line and frame data as the AL440 data
    is clocked in sequentually.

    Unless my software counts the end of a frame and send the line and frame
    info withing the code

    Any other thoughts you have would be appreciated.

  7. Hi Joe, (please dont top post)

    Those dreadfull philps data sheets, I tried to figure out if the SAA
    will generate sync pulses for you, and it can be used in Master mode,
    I think, check section 7.4 on the 7120. But the 7120 needs a parallel
    video data input, and you are using serial flash, seems a bit of a
    messy way to do it,

    My brain hurts, need coffee

  8. Hi Martin,

    My read up of the BT601 standard says you put the Synch pulses in the data
    stream and the BT656 is the parallel interface standard.... to transport the
    BT601 data.
    (obviously parallel is faster than serial and needs to be 13.5MHz, and
    serial would need to be 8 times this speed for 8bit).

    The picture frame will be stored in memory (weather serial or parallel) and
    the micro is used as the mechanism by which the video data from flash is
    written to the video buffer.
    The output of the video buffer is 8bit parallel transmitted to the SAA712x.

    The input side of the video buffer can be slow written data and the output
    side can be at full 13.5MHz.

    I could use a parallel flash and a clocked CMOS 4040 to clock the address
    range of the flash through the video data.... but a micro gives me the
    flexibility to load the video data/memory by serial, SD card or other

  9. Thanks
    I have been reading the book Video Demystified by Keith Jack

    720 samples of video that are composed of Y and Cb /Cr 720x2 = 1440
    byte samples per line.

    I can probabaly wite code in the micro to fill in the synch and frame data
    from lines 1 to 22 and 311 to 335 and 624 to 625

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day