Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!news.swapon.de!eternal-september.org!feeder.eternal-september.org!mx02.eternal-september.org!.POSTED!not-for-mail From: mmphosis Newsgroups: comp.sys.apple2 Subject: Re: Vertical BLanking (VBL) for Apple II Date: Sun, 1 Feb 2015 18:56:46 +0000 (UTC) Organization: Mac GUI Lines: 11 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 1 Feb 2015 18:56:46 +0000 (UTC) Injection-Info: mx02.eternal-september.org; posting-host="ac9e0e4d7dd3957fb97803ee6801bab8"; logging-data="5992"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18suRBOA/63GrSvyLmIfJer" User-Agent: Mac GUI Usenet In-Reply-To: Cancel-Lock: sha1:6FUT5S5E1JrSXXOUiV42mszyvGQ= Xref: csiph.com comp.sys.apple2:23777 I've updated the VBL detection routine. Reading Understanding the Apple II by Jim Sather helped. The routine is much more elaborate than I would have liked, but I think that it works now. There is probably a simpler method using a different graphics mode, but those methods may have their own problems in scanning memory. An added feature of this updated routine is that it restores the HGR screen. This may be more useful than ending up with a cleared HGR screen as was done in the original routine.