Is possible to TURN OFF VDC displaying?

[MIRKOSOFT]

Hi!


I have maybe crazy Q.
As is possible to turn on/off VIC-IIe 53265 gets val 27(value at startup)/0, is possible to do this with VDC displaying on screen?


Why?
Yes, no problem to switch monitor. But I think if is possible to turn off displaying VDC computer can be faster and also if I'm using VDC-RAM only for data (e.g. 64kB buffer), I don't want to see miscellaneous characters / any fragments of overwritten charset when I switch monitor... when I want full 64kB buffer also attributes will be changed, so, it's not possible to will it of zeroes.


Don't you know real turning off VDC display?
(like 2MHz mode when is used command FAST turns off VIC-IIe).


Many thanks for every reply.


Miro

[LokalHorst]

One way would be to play with the VDC-registers 34 (display enable begin) and 35 (display enable end), but it won't speed up the C128 because the VDC doesn't stop the CPU to refresh it's screen.

[commodorejohn]

As LokalHorst said, the VDC doesn't steal cycles from the CPU the way the VIC does, so turning it off won't make the computer any faster. If you need speed on a 128, one thing you can do is to turn on 2MHz mode outside the visible area of the screen; that should make a much bigger difference than turning off either of the video chips would.

[LokalHorst]

Just remembered - you can speed up the VDC itself by setting the DRAM refresh-rate to 00 (VDC Reg. 36) - this leads to a slower refresh and the VDC is less often interrupted while doing block operations. (screen clear for ex.)

[BigDumbDinosaur]

And, guess what?  80CDM has a function to blank the VDC display to prevent static image burn-in.