[Coco] (no subject)

Dave R in Illinois lazyhand at sbcglobal.net
Sun Jan 13 19:10:30 EST 2008



So If I understand correctly, faster memory would help a tad with simple 

calculations but when it comes to anything being drawn on screen, the 

GIME is the limiting factor, not the ram. Interresting. Reason I ask is, 

I was interested in building a coco from scratch, similar to CoCoZilla, but

Replacing the 6309/6809 with a Freescale 68HC11 to lower part count.



Thanks a bunch :D







I *think* I have some 120ns stuff in my 2nd coco3 with a half meg board in
The 2 megs kit in the main one is 90ns I think. Those both work ok and the 
90ns stuff runs dead cold at the actual clock speed it is being run at. I 
can toss a furniture blanket over it with a photo thermometer under it, and 
the temp rise after several hours is 2 degrees. It also has a 63C09 in it 
and is running on an old AT power supply wired externally. But it isn't the 
memory speed that controls the coco's speeds, its the 'dot' clock speed
tied to the display standard where the machine was intended to be used. That

is in the general area of 14.3 mhz, and is further divided by either (IIRC)
for the 3's, and 16 for the originals and 2's to get the actual cpu clock of

(for NTSC, PAL is slightly different) 0.889 mhz for the 1's and 2's, and
mhz for the 3's. 

A side comment here, applicable to the 63C09 equipt machines. The cpu is not

the limiting factor for speed, the gime is. Its output drivers are so puny 
they simply cannot drive a memory interface line fast enough to make use of 
faster memory. What we really, really need, is a replacement gime made with 
modern cmos technology. And thumb our nose at the FCC who mandated the noise

abatement design that made it so in the first place, combined with Tandy's 
refusal to apply a shielding scheme that might have actually worked. But I 



>On Saturday 12 January 2008, Lazy wrote: 

>>Would upgrading the memory in a Coco 2 from 20ns to 10ns provide a 


>>noticeable difference in speed? 


>Since memory speed of the original was about 250ns, and the cycle itself is

>much longer than that, no. And it may lead to troubles using memory that 

>fast in a circuit designed for 10x slower speeds as the faster memory may 

>suffer from noise glitches the slower stuff ignores. 






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