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: REU Hacking.
Message-ID: <2869@csd4.milw.wisc.edu>
Date: 10 Jun 89 06:26:04 GMT
References: <2451.247F6F5D@isishq.FIDONET.ORG> <7028@cbmvax.UUCP> <2720@csd4.milw.wisc.edu> <7074@cbmvax.UUCP>
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Reply-To: jgreco@csd4.milw.wisc.edu (Joe Greco)
Organization: Starbase 74 - Starfleet Operational Support Services
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In comp.sys.cbm article <7074@cbmvax.UUCP>, fred@cbmvax.UUCP (Fred Bowen) wrote:
]In article <2720@csd4.milw.wisc.edu> Joe Greco writes:
]> A few months ago I had been discussing the feasibility of hooking up
]> two REU's to a single machine (64) by remapping one unit to another I/O
]> location (and not $DE00, since I need that as well).  I built the
]> needed decoder to decode the entire $Dxxx region into pages, and
]> hooked in a 1700 at $D500 (1750 at standard address).  It didn't work,
]> it strangled any data stored or fetched.  Not only that, but it was
]> nasty about it.   [...]   A simple stash/fetch appears to work to either
]> unit, but loading up something like RAMDOS fails miserably.
]
]It is possible (meaning, I have done it) to modify an REU by moving its
]select from IO2 to IO1 (simple cut and jumper).  It works fine as you indicate,
]even works with the RAMDOS after I re-assemble the RAMDOS to change the REU's
]DMA controller address (an option you obviously could not attempt :-).  I have

The $100,000 question is: what else would you use an ML monitor
for....  heh.  No, I haven't tried it.  Not even interested.  *MY*
software is entirely flexible in regards to REU location.

]not modified the REU to work with *two* drives though.  Of course, you cannot
]preconfigure both REU's to trigger when $FF00 is addressed, simultaneously.  I
]think this is probably what happened to you, otherwise I don't see what the
]problem is (assuming your decode circuitry is correct).

That is and yet is not the answer I wanted.  You are saying that it
should work.  My experience says no way Jose.  :-)

I am not using that $FF00 trigger business.  There may be some point
on a C128, but on a 64 it would be a half-***ed option and I can't
imagine any real use.

I cannot use IO1 because my *trusty* MSD IEEE interface resides there.
In reality, just a 6526 sitting pretty on IO1.  I can reassemble my
drivers for it to work elsewhere, although it seems like unneeded
work.  

Here's what I did for decoding.  Electronically, I cut 1Y0 and 1Y1
(pins 4 and 5 of U15 74LS139 decoder chip for $Dxxx range) and added a
second 74LS139, duplicating the way 1Y3 goes into the second half of
the original 74LS139.  1Y0 of #1 goes to EN1 of #2, 1Y1 of #1 goes to
EN2 of #2.  A8 and A9 go to both halves of #2.  VIC and SID signals
are taken from 1Y0 on decoder #2 and 2Y0 on decoder #2, respectively.
Moronic Digital Electronics 101 in simplicity; I duplicated a known
solution.  :-)

Electrically, I popped a socket on the motherboard.  Then I took a
little prototyping board and popped three 16 pin sockets on.  Decoders
in two, and a DIP ribbon cable to plug into the motherboard.
Freestyle wiring on the outboard decoder finished it off.  Filter
caps, etc as needed.  All very straightforward, and the 64 runs.
Remove either decoder, and it doesn't.  So both are in use, and my
meter says that all the electrical seems to be cool.

So I cut off IO2 on the last slot on my 5 slot expander, and wire it
to the $D500 decoder line.  Confidently, I plug in a 1750 to the 5th
slot, and a 1700 into a normal slot.  I don't recall specifics, but it
didn't work.  I believe it powered up, but wouldn't run a darn thing
from REU.

Then I tried the DMA line hack, as I already mentioned.  It worked
*better* (I was able to mutilate data at very high speeds, but it DID
transfer!) ...  then I gave up, since the only other line I saw the
REU making use of was BA ("special" lines, that is).

I cannot figure out what is the matter.

Ah well, such is life.

(Time to go check my decode circuitry, maybe?)
--
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