Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!psuvax1!psuvm!art100
From: ART100@psuvm.psu.edu (Andy Tefft)
Newsgroups: comp.sys.apple2
Subject: Re: Display Softswitches
Message-ID: <90296.123137ART100@psuvm.psu.edu>
Date: 23 Oct 90 16:31:37 GMT
References: <2142@unsvax.NEVADA.EDU> <15593@reed.UUCP>
Organization: Penn State University
Lines: 14

In article <15593@reed.UUCP>, reeder@reed.UUCP (Doug Reeder) says:
>
>_VBL       read vertical blanking                C019
>_the screen contents when the high bit of VBL is clear.
>
>    Note, however, that this won't work on a IIc, because Vertical Blanking
>is available only as an interrupt.  (And what fun it is to have a source of
>regular interrupts!)

Not exactly true. The VBL does work differently (as I found out
the hard way) but Dave Lyons sent me a preliminary tech note
that explained it. Apparently the difference is you first have
to enable the vbl; you also have to reset it once you poll it if
the high bit is set.