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OBEX VGA 1280 x 1024 object and changing sync polarity — Parallax Forums

OBEX VGA 1280 x 1024 object and changing sync polarity

AG5ATAG5AT Posts: 5
edited 2014-07-23 19:47 in Propeller 1
A group of us have some spin code that uses VGA 1280x1024 Tile Driver w/Cursor that Chip wrote. I have discovered that the monitor that I would like to use with it uses positive polarity for both Horizontal and Vertical sync. I am using a Samsung 913T. It seems to fall back to 1024 x 768 which only shows me about 2/3s of the screen vertically. Width wise it is ok.

This is mostly a question to Chip since he wrote the code. Is it possible to change the the code to use positive sync?

August

Comments

  • kuronekokuroneko Posts: 3,623
    edited 2014-07-21 16:49
    FWIW, the driver is using positive sync polarity (already), IOW idle state is low for both lines.
  • Cluso99Cluso99 Posts: 18,069
    edited 2014-07-21 19:36
    IIRC there are 2 bits that represent the sync. These are added to each 6bit VGA values (they are normally 00).
    So, if you want to try it, you will need to reverse one/both of these bits.

    But, to see if it that is the problem, add an inverter 74LVC04 to the output circuit might be the easiest solution. (74HC or 74LS would also work).
  • AribaAriba Posts: 2,690
    edited 2014-07-21 20:40
    If your monitor does not recognize the right resolution the reason may be that Chips driver often don't use the standard pixel clock frequencies.
    My VGA monitor is picky about that and I had to modify nearly all older drivers to get them working (Kuronekos drivers work normally out of the object) .

    I have no version of the 1280x1024 driver because my monitor only goes up to 1024x768. If you want to try it search in the Web for the standard pixel and Vsync frequency and modify the constants at begin of the drivers until you find some values that work. But it may be that you don't reach the standard pixel frequency with the Propeller it will be very high for 1280x1024.

    If you just try to get a 80 column display then there are other VGA drivers which use simpler fonts and not so many cogs.

    Andy
  • AG5ATAG5AT Posts: 5
    edited 2014-07-22 17:07
    samsung913t.jpg
    sun-wide.jpg


    Thanks for the info on the 2 bits. I have added 2 attachments to show what the samsung looks like and what I should see from another monitor that has no issue.

    Thanks,

    Aug
    samsung913t.jpg
    1024 x 768 - 140K
    sun-wide.jpg
    1024 x 768 - 178K
  • kuronekokuroneko Posts: 3,623
    edited 2014-07-22 17:25
    @AG5AT: To rule out a frequency issue, can you try the driver listed here http://forums.parallax.com/showthread.php/147505-FYI-320x256-(SXGA)-custom-driver-(single-cog)? It's not quite 108MHz (106.6MHz) but no-one complained so far.
  • AG5ATAG5AT Posts: 5
    edited 2014-07-23 19:34
    I did your requested experiment. I have video. Attached is a picture.

    test-example1.jpg
    test-example1.jpg
    1024 x 768 - 168K
  • AG5ATAG5AT Posts: 5
    edited 2014-07-23 19:36
    I looked at the code, but unfortunately, I don't see where the sync bits are generated, etc buried in the prop assembly.
    It won't be very easy to insert an inverter on the circuit board.
    Aug
  • kuronekokuroneko Posts: 3,623
    edited 2014-07-23 19:44
    AG5AT wrote: »
    I did your requested experiment. I have video. Attached is a picture.
    Yes, looks like 40x32 to me. So it looks like your monitor - while getting the width right - somehow objects to overall timing (Parallax's driver is using 100MHz pixel clock).

    So what are you really after? Resolution or this particular driver?
  • kuronekokuroneko Posts: 3,623
    edited 2014-07-23 19:47
    AG5AT wrote: »
    I looked at the code, but unfortunately, I don't see where the sync bits are generated, etc buried in the prop assembly.
    It won't be very easy to insert an inverter on the circuit board.
    Why would you want to do that? They do have the right polarity (in both drivers).
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