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: <3085@csd4.milw.wisc.edu>
Date: 23 Jun 89 22:20:59 GMT
References: <89061907384920@masnet.uucp> <3028@csd4.milw.wisc.edu> <7107@cbmvax.UUCP> <3041@csd4.milw.wisc.edu> <7116@cbmvax.UUCP>
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Reply-To: jgreco@csd4.milw.wisc.edu (Joe Greco)
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In comp.sys.cbm article <7116@cbmvax.UUCP>, fred@cbmvax.UUCP (Fred Bowen) wrote:
]In article <3041@csd4.milw.wisc.edu> Joe Greco writes:
]>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!
]
]	This is not a will work / won't work thing- there are
]	really close timing factors involved.  It also depends
]	upon the vintage of your C64.

So, what is the "fix" and what versions of the REU and C64 require it?
I have a C1700 REU  Assy 311751 Fab 311753 with an older DIP style 8725 (R1).
	 C1750 REU  Assy 312533 Fab 312535 with a newer "square" 8726 (R1).

Not sure if that first one is an 8725 or 8726...?

The C64 is (C)1984  Assy 250425  with an (R8) VIC and (R1) PAL chip.
Hope that's enough to indicate just how vintage it is or isn't.

]> [...] 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.
]
]	Right you are- I apologize for not looking more closely.
]	The ribbon cable is still a bad idea timing-wise.  Although
]	I'm sure what the situation is, you have not made things

It was the easiest way to interface the "daughterboard" decoder.  I
could probably get it to sit right ON the 64 motherboard, though.

]	clear:  When both REUs are connected, do they both fail to work?

Both fail to work.  At least, my observation was that the relocated
1700 at $D500 mutilated data, and a copy of RAMDOS that usually worked
fine wouldn't load into the 1750 at $DF00.  I didn't bother to see
what the one at $DF00 was doing - it seemed apparent enough that
neither was working too swiftly.

]	If not, which one works?  When only one REU is connected to the
]	ribbon cable, does it work?  Just for the heck of it, try 'em
]	without the ribbon cable, and without the resistor at R4.

The 1750 at $DF00 is working like a charm, with the entire decoder in
place.  What is the "the resistor at R4" supposed to mean?  The C64's
R4 is in the cassette circuitry, and I don't see a marked R4 on the
1700 (one unmarked resistor could be it, though).

]>But, still, did you run two REU's or were you just relocating ONE?
]>That is the $1,000,000.00 question.
]
]	Gee, the price keeps going up :-)   Okay- I have both REUs
]	connected and functioning properly (pay up :-).  Perhaps your
]	C64 is old enough that you are hosed.  Perhaps there is some
]	loading problem hanging all that stuff off the dot clock.

Ah he**, I don't have the equipment or experience to mess with loading
problems and anything else less-than-obvious.

]	Perhaps I'm out of ideas.  I suggest we continue this discussion
]	via email.

Okay, I think I'll take my wonderful BBS down and mess with it some
more tonight.  If you have got it working, that leaves some hope - and
that was the answer I wanted, that SOMEBODY had got it to work!

Thanks for your time and trouble in this, I will scream and moan after
I try some other things and they don't work.  :-)
--
jgreco@csd4.milw.wisc.edu		Joe Greco at FidoNet 1:154/200
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