RE: 6569 luminances

From: Baltissen, GJPAA (Ruud) <>
Date: Wed, 16 May 2012 08:02:37 +0200
Message-ID: <>
Hallo Patryk,

> Could be used as a test / starting point but extra bits
> would have to be added.

IMHO you haven't understood me. By demirroring the VIC and SID you have
created the room to add those extra bits. A part can be used to add
extra I/O, for example a 6526 that gives you the bits to select the
wanted Kernal, other parts give you room for RAM and ROM. To be honest,
this idea is not mine, has been published in a 64er.

But the 64er did the demirroring on the board, something you don't want
to do. Now use the technique (partly) used on the 6502-RAMROM. First you
have to detour the address lines A13, A14 and A15 and the R/W line by
using a 157 multiplexer: the output is connected to the original lines
on the board, side A is connected to the mentioned lines of the CPU and
side B is connected to +5V. 
The moment you address anything that isn't on the original board but on
your board, you switch the 157 to side B and the original board starts
to read from the original Kernal or underlaying RAM. (Why the Kernal?
Any 'safe' address can do. Reading the VIC could wipe information you
could need later and therefore I don't consider that as a safe address)
To avoid bus collisions, add a 245 bi-directional buffer in the data bus
between the original board and yours. 

Use a PAL/GAL to tell the 157 when to detour the original signals or
not. If you use a CPLD, you can incorperate the mentioned 157.

You want more Kernals, different CHARROMs and/or BASICROMs as well?
Place them on you board! You can program the GAL/CPLD in such a way that
the system starts up from the ROM on your board: there you have your
menu. And your menu enables you to choose the wanted Kernal, or
whatever, by manipulating the 6526. 
Adding extra RAM in the demirrored area has its advantages: when a
certain value has been read from a reserved place, the menu program
skips itself and starts up a pre-choosen Kernal.

One more idea: connect the NMI and/or IRQ line to the CPLD and start
emulating freezers and other carts!

I hope this was clear enough :)

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Received on 2012-05-16 07:00:05

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