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From: knudsen@ihwpt.UUCP
Newsgroups: comp.sys.m6809
Subject: 512K and wimpy GIME chips
Message-ID: <1404@ihwpt.UUCP>
Date: Fri, 13-Feb-87 13:43:39 EST
Article-I.D.: ihwpt.1404
Posted: Fri Feb 13 13:43:39 1987
Date-Received: Sat, 14-Feb-87 15:37:56 EST
Organization: AT&T Bell Labs, Naperville, IL
Lines: 35

I bought a blank PBJ upgrade daughter board for my Coco III
and put my own chips in it.  Like, three different brands--
Western Electric, TI, and some Korean outfit.
It hardly worked at all.  I had more Korean chips so I
made it all Korean (they should feel at home in there ;-) ).
Now it almost works -- fine as a Coco II, but usually
screws up if it tries to print much in WIDTH 40 or 80.
Not looking forward to running OS9-L2 on this....

The failures were "analog" in nature -- the more RAM chips
I replaced with Korean, the better it worked.
From this I conclude that some RAM chips must load down
(draw current from) the address and control (RAS, CAS)
and data lines than others.  All these chips are 150 ns
(the PBJ instructions say to use 120ns, but their populated
boards come with 150 chips anyway!)

Originally the GIME chip must drive only 4 chips worth of
address & control, but you multliply this by 4x when you
upgrade.  So I suspect the GIME, which uses wimpy (non-TTL)
CMOS logic, can't drive all those inputs.

Unless you're careful to use exactly the right make
& model of RAM chips.  Anyone got any recommendations?
BTW, the power supply regulator (big heat sink) gets pretty
toasty.  I intend to 'scope out the +5V supply to make
sure there's no ripple.  And of course to view the signal
leads as well.

Cuda been worse -- I cuda soldered all those chips piggybacked
onto my DISTO Ramdisk (which works great, BTW).  Or onto
an Atari 520ST... ... mike k
-- 
Mike J Knudsen    ...ihnp4!ihwpt!knudsen  Bell Labs(AT&T)
>>>DRUGS are for WIMPS who can't handle SCIENCE FICTION<<<