RE: More CPLD explorations

From: Bil Herd <>
Date: Wed, 26 Feb 2014 10:14:44 -0500
Message-ID: <>
I used to tell my guys that if they weren't making mistakes they weren't
going fast enough and were also probably getting too much sleep.  The
standing rule was you could only sleep if a technician was rewiring the
module you were working on.

-----Original Message-----
[] On Behalf Of Marko Mäkelä
Sent: Wednesday, February 26, 2014 12:59 AM
Subject: Re: More CPLD explorations

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 16:00:07

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