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PostPosted: Thu Jul 26, 2007 2:54 pm 
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Joined: Sun Jun 03, 2007 6:43 am
Posts: 130
Location: Rethan Manor, Balmora, Hlaalu District
RR can be accessed on a Commodore 128 as an external ROM. Activate it in the monitor and see for yourself:

>FDE00 0
M88000

This will display the beginning of the active ROM bank. The cart will still show only an 8-kilobyte window, but the configuration registers work normally, and you can bank in any ROM or RAM windows you wish.

It is even possible to program the FlashROM in 128 mode! I did this when I was testing the programming routine I wrote for my flasher. However, writing the Retro Replay RAM doesn't appear to work.

Since the cart appears at $8000, you could even use it as a C128 Function ROM. Special processing is needed with the 8K banking, but if you set both jumpers, you can access the whole 128 kilobytes of the ROM.

Normally the maximum size for a Function ROM is 32 kilobytes, so this would allow much more features for a C128 cartridge. In BASIC, the external system ROM can be seen in banks 8 to 11.

Finally, here is a magic number: 42! That is $2A. Write this into the MMU configuration register to switch external ROM on. You will also get I/O at $D000-$DFFF, first 32K is RAM0 and other areas remain undefined.

PS. Vice doesn't emulate this behavior.

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Commodore 128 Programmer
City of Kouvola, Finland

http://mydarkgothvampiricplace.endofthe ... Commodore/


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PostPosted: Sun Jul 29, 2007 3:19 pm 
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Joined: Wed Jan 11, 2006 12:22 pm
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Really cool discover indeed! Time to start hacking, guys! :)


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