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

Gene Heskett gene.heskett at verizon.net
Tue Jun 28 14:43:30 EDT 2005

On Tuesday 28 June 2005 13:31, Mike Pepe wrote:
>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.

I don't think there is anything wrong with the idea Mike.  Almost any 
simm could be used as long as its still a 9 bit refresh.

However, to do a 2 megger kit requires a bit of hackery around the 
gime to add the 2 additional bits to its internal dat register, Tony 
did it with std TTL chips in his 2 meg kit.  Works great, I have one.

Cheers, Gene
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 soap, ballot, jury, and ammo. Please use in that order."
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