mattd@Apple.COM (Matt Deatherage) (03/26/89)
[Note to the NetMasses: Although I personally believe that responding to each message as it's read is worse and more disorganized than posting a summary message when I'm done reading, the summaries tend to have undescriptive subject lines (esp. when talking about lots of things), so I'll try this for a while.] In article <8903240152.aa08729@SMOKE.BRL.MIL> V131Q5CG@UBVMSC.CC.BUFFALO.EDU (John Taylor) writes: >Topic #1: Vertical Blanking Interval > > Recently there was some talk of this and I kept forgetting to throw >my two cents in, so here it is: If location -16359 is >128 then a >screen-refresh is happening; <128 means the vertical blanking interval is >occuring. > Of course, this probably dosen't apply to the GS and it's probably >been mentioned already (and I missed it) so my two cents is reduced to a >peso or a ruble or something... > Let me quote IIgs Technical Note #40 (in its entirety): "Applications can accomplish smooth animation on the Apple IIgs, Apple IIe, and Apple IIc by changing the data on the screen during the time the system blanks the screen for vertical retracing. You can determine the state of the VBL signal by reading location $C019. "On the Apple IIgs, the $C019 sense of the VBL signal differs from the IIe and IIc. On the IIgs, the screen is blanked when the most significant bit of $C019 is _high_ (greater than 127 or $7F), while on the IIe and IIc, the screen is blanked when the bit is _low_ (less then 128 or $80). "A VBL interrupt also is available on all three Apple II systems via the Apple IIgs Miscellaneous Tool Set or mouse firmware, the Apple IIe mouse card, and the Apple IIc mouse firmware." ============================================================================== Matt Deatherage, Apple Computer, Inc. | "The opinions expressed in this tome Send PERSONAL mail ONLY (please) to: | should not be construed to imply that AppleLink PE: Matt DTS GEnie: AIIDTS | Apple Computer, Inc., or any of its CompuServe: 76703,3030 | subsidiaries, in whole or in part, Usenet: mattd@apple.com | have any opinion on any subject." UUCP: (other stuff)!ames!apple!mattd | "So there." =============================================================================