Date   : Fri, 26 Jan 1996 23:38:47 +0000 (GMT)
From   : Tom Seddon <T.W.Seddon@...>
Subject: Vertical blank interrupt

I am aware that the vertical blank interrupt occurs 50 times a second, but
I am unsure as to when it occurs. Does it occur when the visible display
area -- that is, 256 scanlines or (display character rows)*(scan lines per
character row) -- has all been traced, or does it occur when all 312
scanlines (ie both visible and invisible) have been traced? Or is it
rather more weird than this? 

Thanks for any help, my system VIA is implemented (although I haven't 
tried compiling the latest version yet) along with keyboard, latch and 
timer support, and I want to get started on the graphics system.

--Tom

     .                     ** Tom Seddon **                     .
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