Join GitHub today
GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.Sign up
PAGE1/2 select occurring 1 cycle early #656
Based on Sather's precise VBL sync (UTA2e, 3-26), I wrote 3 similar tests:
Each test does a "Sather precise VBL sync"; waits 17 (or 18 or 19) cycles, then:
So it appears that there's no delay for the PAGE1/PAGE2 switch!
Side-note: Is this the same behaviour on an Apple II+? And what about DGR/TEXT80? (eg. Ansi Story) And LORES/HIRES?
btw. that glitch (on line-7) switching from GR back to TEXT is explained in Don Lancaster's "Enhancing your Apple II & IIe, Volume 2", on page 221 it says:
"Glitches are far simpler to manage on the lIe. Just exit from text on a space and exit from LORES black, and all lIe glitches should be invisible."
And also see Volume 1, page 244:
"Usually, there is no problem in going from TEXT to HIRES, from HIRES to TEXT, from LORES to HIRES, or from HIRES to LORES. But you can get glitches on a TEXT to LORES or a LORES to TEXT transition. Here's the rule to stomp these glitches ..."
Hi Nick - my suspicion about this extra cycle for switching between TEXT and LORES is something funky going on with 7M and 14M clocks (maybe?).
So maybe 1 extra cycle for 7M/14M change?
Anyway, I don't think emulation of this "glitch" is important, but clearly the timing of it is.