[Coco] 64 K upgrade for COCO 1 gives ?OM ERROR
Bruce W. Calkins
brucewcalkins at charter.net
Sat May 2 18:26:51 EDT 2020
"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.
OTOH; late CoCo 1with a non-chicklet keyboard should be a "285"/"F" board.
The high low jumper was for selecting the upper or lower bank of
"half-good" 64k chips.
It begins to sound like a bad RAM chip, or perhaps a bad jumper or some
other "little" detail.
This book link might help; <www.roust-it.dk/coco/littlewonder.pdf>
Starting with page 82.
It does state that the jumper on the "285"/"F" boards were labeled 16/64 K
On 5/2/20 6:00 PM, John E. Malmberg wrote:
> I have a COCO 1 later grey case with the non-chicklet keyboard.
> It was has a 16K memory badge.
> While the computer had 16 K memory in it, I was able to verify that it
> had BASIC 1.1 ROM in addition to the ECB ROM.
> I tried to put 64 K using 2164 memory chips.
> The circuit board had 4 jumpers to move to go from 16 K to 32 K, which
> I moved to the correct locations.
> The circuit board has a jumper set labeled high / low.
> The computer boots, displays the sign-on for Extended Color Basic 1.0.
> It reports ?OM ERROR for any command given.
> Any ideas?
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