grx0644@uoft02.utoledo.edu (02/19/91)
I am posting this off of the Commodor@ubvm listserv for Cory, who can not post
currently due to some system problems over there.
Tony
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Subj: REU expansion
Okay, I posted a couple of questions about this before, but they seemed to fork
off into discussions completely unrelated and I never even got an
acknowledgement of the major content of the questions (as far as any sort of
answer to the questions). So hopefully this time, someone can help me out.
Okay, I got a 1700 REU from someone (he may let me keep it FREE). I want to
upgrade it to 512k since 128k is useless with GEOS and not much better with
anything else.
I did use it for a 128k expansion for a while but things I did with it didn't
work quite right. DesTerm didn't like it. Maverick and Copy II 64/128 copies
made with it didn't work. Other problems. I checked it with the Maverick REU
checker and it told me the REU was bad. So my first (and most important
question) is this: Would it most likely just be a bad DRAM chip or could it be
the controller chip? If it's just the DRAM then upgrading should give me a
good 512k right? But if it's the controller, can I get a new controller chip
to use with the new 512k? If so, where and how much? I REALLY want to upgrade
this to a 512k rather than buying a new 1750 clone since the 1700 is FREE (or
at least VERY cheap) and I can get the chips to upgrade for about $15 (maybe
less) through an Electrical Engineering professor. THANK YOU VERY MUCH FOR ANY
HELP ON THIS.
Second question (and just curiosity): If all we have to do to upgrade to 512k
is to replace the chips that were there with 256k chips, then why do we have to
go through all that trouble to go beyond 512k? Why can't one just buy 512k
chips to get 1MEG or 1MEG chips to get 2MEG? I don't know anything about how
this stuff works other than enough to do the replacement of the chips so if
anyone can tell me this, I'd appreciate it.
Thanks again.
Doctor WHO
(Cory Hug)
83882319@UWPLATT - Bitnet
83882319@UCS.UWPLATT.EDU - Internetbhelf@athena.mit.edu (Bill Helfinstine) (02/20/91)
In article <1991Feb19.105218.2939@uoft02.utoledo.edu> grx0644@uoft02.utoledo.edu writes: > >I did use it for a 128k expansion for a while but things I did with it didn't >work quite right. DesTerm didn't like it. Maverick and Copy II 64/128 copies >made with it didn't work. Other problems. I checked it with the Maverick REU >checker and it told me the REU was bad. So my first (and most important >question) is this: Would it most likely just be a bad DRAM chip or could it >be the controller chip? If it's just the DRAM then upgrading should give me a >good 512k right? But if it's the controller, can I get a new controller chip >to use with the new 512k? If so, where and how much? I REALLY want to >upgrade this to a 512k rather than buying a new 1750 clone since the 1700 is >FREE (or at least VERY cheap) and I can get the chips to upgrade for about >$15 (maybe less) through an Electrical Engineering professor. >THANK YOU VERY MUCH FOR ANY HELP ON THIS. > Okay, first, if a chip is bad in your REU, chances are it is a RAM chip (there are 16 RAM chips and only one controller chip). A way to be certain is to run a test with the STASH and FETCH commands from BASIC. If it brings back scrambled data from the REU, it is probably a RAM chip. If it doesn't do anything at all to memory, it is probably the controller. If it turns out to be the controller that is bad, the only place you could get a new one is from Commodore, I would guess. It is a highly customized chip designed specifically to interface to Commodores and do DMA transfers. The only other possibilities would be a reseller of Commodore chips like Jameco or that place in New York that I forget the name of, but I don't recall either one listing them. Maybe a service center would have one, but don't count on it. >Second question (and just curiosity): If all we have to do to upgrade to 512k >is to replace the chips that were there with 256k chips, then why do we have >to go through all that trouble to go beyond 512k? Why can't one just buy 512k >chips to get 1MEG or 1MEG chips to get 2MEG? I don't know anything about how >this stuff works other than enough to do the replacement of the chips so if >anyone can tell me this, I'd appreciate it. Well, first of all, there are no such things as 512k chips. Since DRAMs have their address lines multiplexed, they essentially have twice as many logical address lines as physical address lines. Thus, no 512k chips, since they would have 19 address lines, when we need an even number. This is why the sequence went from 1k to 4k to 16k to 64k to 256k to 1M to 4M and on into the future. Secondly, 64k and 256k chips are both 16 pin beasts. The only difference in their pinouts is the 256k chip has a multiplexed address line where there was an unconnected pin on the 64k chip. This makes it very easy to make an REU that can take 64k or 256k chips, just needing a jumper change to access the additional space. 1M chips, on the other hand are 18 pin chips. This would require a complete board redesign, which is why the REU-fattening project uses lots of 256k chips stacked up on top of each other. > >Thanks again. > > Doctor WHO > > (Cory Hug) > > 83882319@UWPLATT - Bitnet > > 83882319@UCS.UWPLATT.EDU - Internet Shore thing. Bill Helfinstine bhelf@athena.mit.edu