Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!apple!dlyons From: dlyons@Apple.COM (David A. Lyons) Newsgroups: comp.sys.apple2 Subject: Re: Pipedream and VBLint Message-ID: <51523@apple.Apple.COM> Date: 15 Apr 91 00:33:31 GMT References: <12837.apple.net2@pro-grouch> Organization: Apple Computer Inc., Cupertino, CA Lines: 27 In article robert-s@cs.aukuni.ac.nz (Robert Sheehan ) writes: >After careful scrutiny of what was going on I found out that the problem was >a piece of code which checked vertical blanking. > >ECD2: bit $C019 > bmi $ECD2 >ECD7: bit $C019 > bpl $ECD7 > rts > >Now as far as I can make out this code should wait for the start and end of >the vertical blanking period (different order according to whether running >on a GS or IIe). > >On my IIc the second test always loops. I fiddled around and found out that >$C019 always returns $1D (I think) on my IIc. Anyone know anything about this? $C019 does not work quite the same on the IIc and IIc Plus as on the IIe and IIgs. See Apple IIc Technical Note #9, November 1990. -- David A. Lyons, Apple Computer, Inc. | DAL Systems Apple II System Software Engineer | P.O. Box 875 America Online: Dave Lyons | Cupertino, CA 95015-0875 GEnie: D.LYONS2 or DAVE.LYONS CompuServe: 72177,3233 Internet/BITNET: dlyons@apple.com UUCP: ...!ames!apple!dlyons My opinions are my own, not Apple's.