[Coco] [Color Computer] 1M simms in Cloud9 SIMM upgrade kit

Mike Pepe lamune at doki-doki.net
Tue Jun 28 13:31:00 EDT 2005

I was going to send this over to Mark at cloud 9, but I figured I'd open 
it to the group.

I'm unsing a Cloud 9 512k SIMM upgrade board. Problem is: I'm out of 
256k simms. I checked the datasheets on 1M DRAM chips to see really what 
the difference is.

256k chips are essentially a 2 dimensional matrix, 512 on each "axis".
(9 bit refresh)

1M chips are also a 2 dimensional matrix, but from what I read they are 
a 512x2048 matrix. (also 9 bit refresh)

With that in mind, it seemed to me that if you simply tie A10 on a 1M 
simm to 0 or +5v, that it should function as a 256k simm. The only 
difference is that only 3/4 of the capacity of the module is unused.

So, that's what I did... I tied A10 of the SIMM modules to ground. I 
installed 1Mx8 modules, and powered up- and it works.

Then I got brave and installed a set of 1M 3 chip modules. They also 
work! I've been running a memory test on it for several hours and no 
problems reported.

Am I missing some detail as to why this may be a bad idea? I have lots 
of 1M simms, and even though it's a waste of 1.5M of capacity I'd rather 
use up what I've got. Plus in theory the 3 chip 1M simms should run cooler.


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