[Coco] 64 K upgrade for COCO 1 gives ?OM ERROR

Bruce W. Calkins brucewcalkins at charter.net
Sat May 2 21:09:44 EDT 2020

On 5/2/20 7:44 PM, John E. Malmberg wrote:
> On 5/2/2020 5:26 PM, Bruce W. Calkins wrote:
> > "E" and earlier boards needed some added wiring to a previously unused
>> gate on a 74LS02 to properly switch the RAM.  Only the "285"/"F"
>> boards  were a direct upgrade.
> It is definitely an E board.
> So I may need more information on how to upgrade this computer to use 
> the full 64K.

I upgraded my "E" board back in "the day."  A little wire-wrapping and 
lifting a pin or two on the 74LS02.  It was my first CoCo upgrade and I 
still remember how my heart was beating with fear that I might kill my 
computer.  I still have that machine, although it wears a J&R Banker 
256k upgrade now.  I know I still have the instructions for that 
original 64k upgrade too, but just where in the midden heap is the question.

Bruce W.

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