NO BORDER IN GFA

     Information for low border overscan in (fully) GFA-BASIC.

     Written by Corsair of      *** * * ***
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               (demo development)

     Hi everybody!!!

     This is the first time that I've sent  an article in. I am a GFA-BASIC
     freak and I thought it would be nice  for  all the GFA coders to get a
     routine for opening  the  low  border.  I've  originally  written this
     routine for the Dutch magazine  'START',  so  it's documented in Dutch
     language.

     (Note from Bonus: already changed in English !)

     Anyway, I tell you in short lines how the routine works: You install a
     screen of 32000+50*160 bytes. (50*160  Bytes  extra because the screen
     becomes  bigger!)  After  initialising   and   turning  off  some  MFP
     interrupts (they disturb everything)  you  can  finally open the lower
     border. First you synchronize  the  shift  with  VSYNC  and some VIDEO
     ADDRESS COUNTERS ($ff8205,  $ff8207  and  $ff8209).  Then  the program
     waits (->> doing other  things  like  putting  sprites etc.). When the
     electron-beam arrives at the last screenline  (200  in low res) and is
     in the right border, you put the  sync  at  60 hertz. And a few cycles
     later back at 50 hertz. Wooooooow!

     Easy eh?

     Oh yeah, I almost forgot: you  can  modify  some syncs by pressing the
     +,-, and arrow keys. And the overscan only works compiled!

     Thanks to Mr Ni! of the  Tos  crew  for  giving  me some hot hints and
     helping me with  his  special  (V)sync  routine.  (This  special Vsync
     routine is not included in the routine)

     Corsair of the Giants.