Article-I.D.: oberon.187
Posted: Thu Jan 23 03:28:29 1986
Date-Received: Fri, 24-Jan-86 22:09:40 EST
Distribution: net
Organization: U. of So. Calif., Los Angeles
Lines: 35

*** REPLACE THIS LINE WI...munchmunchmunch

I really need a good description of exactly why is it that the Amiga will
flicker in the 400 mode.  I understand Television reasonably well, enough
to understand that television is a set of 60 fields of 262 lines of video
which extend from the above the top of the visible portion of the screen
to just below the bottom. There is 1/60th of a second worth of motion and
then the next frame is drawn, this time the lines are drawn between the
previous lines.  This process is done so as to keep the screen from fading
before the electron beam gets to the bottom of 512 lines after a 1/30th
of a second.  When the Amiga is in 200 mode I assume that it is drawing
on the first field and then not on the second?  Or is it drawing every
forth line and in the second field it will pick up the middle of the
remaining 3?  If the IBM pc only has 200 lines why is it that there is
not such a noticeable dark line on the undrawn line, how about the C64?
I had always assumed that it was just repeating the lines to fill up
400 lines worth of space.
Perhaps the real problem that I could not figure out in my own head is,
if the Amiga had to flicker to remain compatible with NTSC, why is it
that even the highest resolution video of the day will not flicker like
the Amiga?  Infact, no one ever mentioned that NTSC flickered to me before,
PAL, sure, the whole 625 lines are drawn before it starts over again,
sort of like a strobe.
Any chance it has to do with unstable sync signals from the Amiga, when
I run Setlace it sure seems to start shaking the formerly rock steady
lines around on the screen.

If this becomes a popular question to respond to feel free to send me
mail, I will post what I learn.

==============================================================================
Randal Spencer      Student DEC Consulting - University of Southern California
Home: 937 N. Beverly Glen Bl. Bel Air California 90077          (213) 470-0428
Arpa: Spencer@USC-ECL  or  Spencer@USC-Oberon          Bitnet: Spencer@USCVAXQ
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