Re: Vertical BLanking (VBL) for Apple II

From	D Finnigan <dog_cow@macgui.com>
Newsgroups	comp.sys.apple2, comp.sys.apple2.programmer
Subject	Re: Vertical BLanking (VBL) for Apple II
Followup-To	comp.sys.apple2.programmer
Date	2015-01-03 07:34 +0000
Organization	Mac GUI
Message-ID	<dog_cow-1420270476@macgui.com> (permalink)
References	<mmphosis-1420157056@macgui.com> <c4c09601-5fda-4f1b-bfb4-4c75a76dc5a9@googlegroups.com>

Cross-posted to 2 groups.

Followups directed to: comp.sys.apple2.programmer

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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/

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Thread

Vertical BLanking (VBL) for Apple II mmphosis <mmphosis@macgui.com> - 2015-01-02 00:03 +0000
  Re: Vertical BLanking (VBL) for Apple II "Bill Buckels" <bbuckels@mts.net> - 2015-01-01 18:10 -0600
    Re: Vertical BLanking (VBL) for Apple II doug.dingus@gmail.com - 2015-01-01 18:32 -0800
      Re: Vertical BLanking (VBL) for Apple II Michael Black <et472@ncf.ca> - 2015-01-02 00:07 -0500
        Re: Vertical BLanking (VBL) for Apple II Michael J. Mahon <mjmahon@aol.com> - 2015-01-02 02:43 -0600
  Re: Vertical BLanking (VBL) for Apple II David Schmenk <dschmenk@gmail.com> - 2015-01-02 17:40 -0800
    Re: Vertical BLanking (VBL) for Apple II D Finnigan <dog_cow@macgui.com> - 2015-01-03 07:34 +0000
    Re: Vertical BLanking (VBL) for Apple II mmphosis <mmphosis@macgui.com> - 2015-02-01 18:56 +0000

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