Re: More CPLD explorations

From: Marko Mäkelä <>
Date: Wed, 26 Feb 2014 07:59:08 +0200
Message-ID: <20140226055908.GA4224@x220>
On Tue, Feb 25, 2014 at 06:27:35PM +0100, Gerrit Heitsch wrote:
>Then the interesting part is how to switch between them without 
>breaking compatibility to existing Software in plain C64 mode. The 
>dilemma the C128 designers already faced and _almost_ solved.

Well, at least the C128 designers made a honest attempt. Had they hidden 
the extra VIC-IIe registers in C64 mode, it would have been even better.

The C65 booted up in C64 mode and used special "port-knocking" sequence 
on the VIC-III to switch to C65 mode.

The suggested change (disable the character generator ROM independent of 
the VA14 and VA15 settings) sounds like reinventing the function of the 
CHAREN bit in C128 mode. IIRC, in C128 mode the CHAREN bit controls the 
visibility of the character generator ROM.

Back on topic: Would it be possible to integrate the DRAM address 
multiplexer on the PLA replacement, and then integrate the functionality 
of the C128 MMU to the PLA replacement? This would allow such features 
as relocating the zero page and the stack. This would be like a poor 
man's C128, without the VDC, Z80, or 2MHz mode.


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Received on 2014-02-26 07:00:02

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