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: D Finnigan Newsgroups: comp.sys.apple2,comp.sys.apple2.programmer Subject: Re: Vertical BLanking (VBL) for Apple II Followup-To: comp.sys.apple2.programmer Date: Sat, 3 Jan 2015 07:34:12 +0000 (UTC) Organization: Mac GUI Lines: 23 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sat, 3 Jan 2015 07:34:12 +0000 (UTC) Injection-Info: mx02.eternal-september.org; posting-host="ac9e0e4d7dd3957fb97803ee6801bab8"; logging-data="14403"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/jQ6X481jR0T5CM6SQs6kT" User-Agent: Mac GUI Usenet In-Reply-To: Cancel-Lock: sha1:kU4lvfW8aUUMqNdSS9z/tUIEMBo= Xref: csiph.com comp.sys.apple2:23407 comp.sys.apple2.programmer:1464 David Schmenk wrote: > On Thursday, 1 January 2015 16:04:20 UTC-8, mmphosis wrote: >> http://hoop-la.ca/apple2/2015/vbl/ > > This is basically the code the MouseCard uses to initialize the 6522 timer > for VLB interrupts on an Apple ][ and ][+. Don't try enabling the VLB > interrupts from code residing in the $2000 to $4000 range, like in a > ProDOS > system program. Ask me how I know :-) High-Resolution Graphics page 1 gets cleared by the mouse firmware so your program gets nuked. I found this out the hard way when writing the Multitasking Mouse Draw Demo. Fortunately, I had an inkling of reading about this side effect long ago, so I pulled out the AppleMouse manual, and sure enough, there was the warning. This memory clear only happens on the original II and II Plus -- ]DF$ Apple II Book: http://macgui.com/newa2guide/ Usenet: http://macgui.com/usenet/ <-- get posts by email! Apple II Web & Blog hosting: http://a2hq.com/