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

j_e_daggett j_e_daggett at yahoo.com
Fri Jul 1 14:49:01 EDT 2005

--- In ColorComputer at yahoogroups.com, "Paul T. Barton" <idezilla at y...>
> Mike,
> Still, I think that it can be done.
> By using CAS before RAS DRAM internal refreshing.
> The DRAMs keep their own internal counter
> for this. Just swap RAS for CAS,
> only during HSync and/or VSync.
> I know that this works, I use it.
> I could give out a partial schematic for this,
> if you want a look-see.
> Paul


you can use CAS before RAS. During that period most page mode drams
allowed ras only,cas before ras and hidden refresh. The problem I see
with CAS before RAS is that you slow the aceess time down by 1/2. That
is a 150 nS access time becomes a 225nS access time dram. The way I
understand dram speed specs is that access time is determined from
when the RAS line gose low and the data is ready for reading on the
read cycle. CAS to data ready is half that of RAS to data ready.
Putting the CAS before the RAS increases access time. In the computer
world where speed is the holy grail, slowing down access is blasphemy. 


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