[Coco] [Color Computer] Re: Difference between 86 and 87 GIME

[j_e_daggett]

--- In ColorComputer at yahoogroups.com, Mike Pepe <lamune at d...> wrote:
> The only difference I'm aware of was corrected timing that fixed some 
> problems with 150nS DRAMs. Is there anything else of significance 
> between the two revisions that makes the 87 really much better than
the 86?
> 
> If you're using 120nS or faster DRAMs, does it matter which version you 
> have?

******

As far as I know there is no obvisous way to tell the GIME chip what
speed the dram is. With that in mind to my knowledge the GIME chip is
set for one speed only. That is for the slowest of dram and that would
be 150 nS dram. Using 120 or 100 nS dram will be still operating them
at 150nS access speed. 

Dram access speeds are speced from the time the RAS line goes low to
the time data is ready for a read cycle. The main timing problem of
the 86 GIME was with Trc. This is the total cycle time of a read or
write cycle. Most manufacturers speced this time at 260 nS minimum.
SOme went has high as 280nS minimum. At  high speed(1.78 MHz) one half
the E clock time is 279nS. The GIME to read from video ram and then
switch the multiplexor back to the CPU address has only 19 nS time to
spare. Any jitter or poor synchronization can cause problems. 

This is an understanding I have of the GIME's operation. There  were
someother internal cleanups that may have taken place in other spots
of the GIME with the 87 version. 

james
 




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