Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!jgreco
From: jgreco@csd4.milw.wisc.edu (Joe Greco)
Newsgroups: comp.sys.cbm
Subject: Re: TWO CARTRIDGES AT ONCE
Message-ID: <3041@csd4.milw.wisc.edu>
Date: 22 Jun 89 01:35:37 GMT
References: <89061907384920@masnet.uucp> <3028@csd4.milw.wisc.edu> <7107@cbmvax.UUCP>
Sender: news@csd4.milw.wisc.edu
Reply-To: jgreco@csd4.milw.wisc.edu (Joe Greco)
Organization: Starbase 74 - Starfleet Operational Support Services
Lines: 71

In comp.sys.cbm article <7107@cbmvax.UUCP>, fred@cbmvax.UUCP (Fred Bowen) wrote:
]In article <3028@csd4.milw.wisc.edu> (Joe Greco) writes:

[...]

]>WHO'S figured out how to hook up two REU's at the same time?  SOMEONE
]>PLEASE TELL ME!  :-)
]
]Sorry, I thought I did tell you :-)  While your special decoding looks fine
]to me (what do I know- I'm not a hardware type), my simple modification of
]the chip select (from IO2 to IO1) works.  I don't believe there is anything
]particularly unique about the IO1/IO2 timing.  If I had the time, I would
]duplicate your decoder hardware and try it.  The only other difference
]between your setup and mine is the computer- I use a C128, you use a C64.
]I trust you have modified the 1700/1750 C128-compatible REUs to work properly
]on your C64.

I've never HAD any problems running 128 REU's on my machines.  You
know the saying, if it isn't broke- don't fix it!

There's nothing abnormal about IO block timing that I am aware of
(more in a minute on that).  

]If your software is so flexible that it works wherever the REU is located,
]I trust your software for the MSD cartridge is too- move it to your newly
]decoded region :-)  Perhaps the additional TTL delay you introduced is the
]culprit.

"My" software for the MSD is actually a rehash of MSD's own code (the
darn thing's EPROM blew up one day).  Still, it wouldn't be hard to
relocate.  But: There *IS* no additional TTL delay, if you understand how
my decoding works.  IO1 and IO2 go through two 74LS139 decoders, my
new IO blocks also do.  The circuitry and timing are identical, with
the possible exception of a one foot ribbon cable I introduced into
the works.  That isn't it, as ONE REU works all by itself.

Actually, I designed my software to work with "several" REU's if need
be, each type of data I am working with can be made to run off of a
different REU address.  Assemblers make the world go 'round....  That
was easy.  The tri-byte arithmetic was a little more painful and
memory consuming.  (Joe begins to appreciate 16-bit processors  :-)

]The scheme I used has worked for others.  One word of warning- the power
]supply is a real issue, so folks who have not beefed up their power supply
]as Joe has should not attempt this, particularly on a C64.

But, still, did you run two REU's or were you just relocating ONE?
That is the $1,000,000.00 question.

And yes, children, don't try this at home unless you have a power
supply rated at SEVERAL amps (even the 1764's might be stressed by
these kind of shenanigans)  :-) :-) :-) :-) :-)


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