What is the poke to turn a C128 to 2MHz in C64 mode?

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Boray
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What is the poke to turn a C128 to 2MHz in C64 mode?

Postby Boray » Thu Dec 02, 2004 10:26 am

/Anders
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carlsson
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Postby carlsson » Thu Dec 02, 2004 12:04 pm

POKE 53296,PEEK(53296) OR 1 : REM $D030

However, since the other chips are not 2 MHz compliant, I think the screen will go blank and the I/O ports will not work until switching back to 1 MHz.
Anders Carlsson

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Boray
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Postby Boray » Fri Dec 03, 2004 5:24 am

Great! Thanks!

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Postby Bacon » Fri Dec 03, 2004 6:02 am

carlsson wrote:However, since the other chips are not 2 MHz compliant, I think the screen will go blank and the I/O ports will not work until switching back to 1 MHz.

True, but if you're programming in assembly, you can set up raster interrupt routines that switches to 2MHz at when the raster beam reaches the bottom border, and back to 1MHz when it reaches the start of the screen. Should give you the equivalent of 1.5MHz or so.

Try out Elite 128 (a version of the classic game Elite modified to run on a 128 in 64 mode) to see the difference in speed when this technique is used. It can be switched between 1MHz and 2MHz in-game, so it's easy to see the effect on the vector graphics animation.
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carlsson
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Postby carlsson » Fri Dec 03, 2004 7:33 am

Yep. Of course it is useful, only that Boray should not expect to get twice the speed on everything in C64 mode.
Anders Carlsson



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Boray
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Postby Boray » Fri Dec 03, 2004 9:50 am

It didn't work in basic! It works in ML in 64 mode and in basic in 128 mode (and of course probably in ML in 128 mode), but the moment you do that poke in basic in 64 mode, then everything stops! Any idea why?

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idrougge
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Postby idrougge » Wed Dec 15, 2004 4:59 am

Bacon wrote:True, but if you're programming in assembly, you can set up raster interrupt routines that switches to 2MHz at when the raster beam reaches the bottom border, and back to 1MHz when it reaches the start of the screen. Should give you the equivalent of 1.5MHz or so.


Isn't that much like how the Plus/4 and C16 work?
C128, C128D, C64, C64C, ABC80, ABC800, ABC806, 130XE, ZX81, Spectrum 48k, Dragon 32, TI99/4A, Laser 200, Spectravideo 328, Sord M5, VIC20...


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