"Vaporlock" technique from Don Lancaster's Enhancing Your Apple II and IIe

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"Vaporlock" technique from Don Lancaster's Enhancing Your Apple II and IIe

I was reading about Don Lancaster's "Vaporlock" technique for finding the exact timing of the vertical blank during screen refreshes.   Does anyone happen to have the sourcecode available or know where I can find the companion disk that came with Enhancing Your Apple II and IIe I am hoping to avoid typing everything in manually

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Joined: Aug 18 2005 - 16:26
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Wow. Thanks for pointing this out

In the mid-80's through word of mouth, I played around with (LDA $C050) what is referred to as the "floating bus", although at the time I didn't know that term. Much much later, I found Bob Bishop's article "Have an Apple Split" from Softalk, October 1982, and others have similar programs that use the floating bus. 

Here is my quick one-liner to see a horizontal video effect:

300:AD 50 C0 EA AD 51 C0 4C 0 3 N 300G

This needs to be run from the MONitor on a real Apple II, or with a cycle accurate emulator like AppleWin, Epple ][, KEGS, ...


I've heard others use the term "vaporlock", so regarding Don Lancaster's book, I was able to find a few things ...

The book on Don Lancaster's web site:


page 204 Enhancement 13 PROGRAM 13-1 Listing of VAPORLOCK.SOURCE.


A disk with the VAPORLOCK binary program without the source code:







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