From: jimc@tau-ceti.isc-br.com (Jim Cathey)
Subject: Re: few video questions
Organization: Olivetti North America, Spokane, WA
Lines: 28

In article <7480224@hpfcso.FC.HP.COM> myers@hpfcso.FC.HP.COM (Bob Myers) writes:
>situation sometimes called "block" sync).  You can generate such a combined
>(or "composite") sync in two simple ways - OR the H. and V. syncs together,
>which gives you the non-serrated "block" sync, or EXOR them, which makes
>serrations.  (Try it!)  Actually, the EXOR doesn't really do kosher serrated
>sync, since it puts the rising (and falling, for that matter) edge of the H. 
>sync pulse off by a pulse width.  But that usually makes no difference.

Sometimes.  It depends on your monitor and your timing.  If you don't
have enough vertical front porch and you use XOR composite sync you can
get even/odd tearing at the top of the screen, which is very sensitive
to the HHOLD control.  It looks like what you would expect if you
scanned the even fields (say) onto a sheet of mylar and had pinched the
upper left corner with your fingers and started to tear it off the tube. 
With proper composite sync (equalizing pulses) the interlace is rock
solid. 

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