Shop OBEX P1 Docs P2 Docs Learn Events
Trying to get a decent PAL video signal — Parallax Forums

Trying to get a decent PAL video signal

Jon87Jon87 Posts: 14
edited 2010-03-30 21:35 in Propeller 1
Hi everyone. I'm new to the propeller chip but i'm finding it easy to use and its very fun to learn.

A problem i'm having is trying to get a PAL video which uses the whole screen and isn't distorted. I followed the programming tutorial in the propeller tool and the NTSC video looks nice although some of the characters look a bit jumpy. I've changed tv_mode to make tv.spin output PAL video but as the video below shows the edges of the red box ripple (although the text looks nicer than the NTSC video). Also, the blue background pulses a little bit (its hard to describe and can't really be seen in the video)

www.youtube.com/watch?v=mDvxrGaVBsk

I also tried a PAL colour bar generater that i found here

I'd like to know if anyone has achieved a nice PAL video which can use the internal font ROM

Thanks
Jon

Comments

  • ColeyColey Posts: 1,112
    edited 2010-03-30 11:26
    Hi Jon and welcome to the forums...

    Clear PAL is possible, try here for some code and inspiration....

    http://forums.parallax.com/showthread.php?p=700697

    http://forums.parallax.com/showthread.php?p=699523

    I'll try and dig some TV_Text code I have when I get home tonight.

    Regards,

    Coley

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    PropGFX - The home of the Hybrid Development System and PropGFX Lite
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-03-30 16:36
    The video really doesn't look that bad. You've got some zipper artifacts (a.k.a. the creepy crawlies) going on, but that may be due to an inadequate comb filter in your monitor. One thing you could try is tweaking the value of _XINFREQ a few Hertz or tens of Hertz to one side or the other of the nominal value. (You'll know when you've gone too far.) Video is very sensitive to small timing inaccuracies, and your crystal may be off just a tiny bit.

    -Phil
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-03-30 21:35
    You will never get an excellent PAL signal unless the subcarrier to horizontal relationship is held ( SCH ). Subcarrier frequency was a kludge from the start, at 1135 x Horizontal plus or minus 25Hz ( can't remember which ).

    The crawlies will always be there, it just whether they are controlled or free running. Broadcast PAL bars has a top to bottom crawler travel, on the green to magenta transition, over 4 seconds. You can follow it down with your finger, but at a distance it is intended to be less obvious. This painting over a monocrome picture method is ok for broad areas, but suffers on fin details such as text and lines.

    The trick of varying the freq contant does improve the beating of the blue background, on my "demoboard" it is better when 4_999_500 is used rather than 5_000_000. I think it is because the Xtal runs slower, but I suspect measuring it might be slowing it a bit more.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Style and grace : Nil point

    Post Edited (Toby Seckshund) : 3/30/2010 9:40:21 PM GMT
Sign In or Register to comment.