[Coco] Dynamic RAM Q

[jdaggett at gate.net]

Mike 

One issue is now finding 74LS785s. LS783s can be had, but the LS785 are even 
rarer than the 63C09s. 

Also Mark McDougal was doing a Coco1/2 in an FPGA. So he probably has some 
code that will do the function of the SAM chip.  The refesh counter can easily be 
modified from 128 cycle in 2mS up to 512 cycles in 8mS if needed. 

james

On 9 Oct 2006 at 11:56, Mike Pepe wrote:

> Phill,
> 
> You know, this problem has already been solved.
> 
> In Rainbow magazine there was a project published for a 256k upgrade. The
> upgrade involved a 74LS785 SAM and 256k memory chips (they need 256 column
> refresh, which the LS785 provides)
> 
> I don't recall the details but I don't believe there was anything more
> exotic than a mux controlling the A9 line for the 41256 chips. Maybe
> someone has the article handy in their collections and can provide us the
> details.
> 
> I do remember the thing was controlled by doing reads of the SAM bits.
> 
> -Mike
>