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

[Paul T. Barton]

j_e_daggett,

You missed the part where I stated that
this CAS/before/RAS refresh was during
video (only!) and during HSync and
VSync. So, no slowdowns at all!
(Must have been on another email,
"somewhere".)

Check the URL:
http://home.wwdb.org/irgroup/scope.html
Shows the timing from a TEK 'scope
during non-screen video time.
(another freebie).

Paul :-) Happy Friday!

--- j_e_daggett <j_e_daggett at yahoo.com> wrote:


> --- In ColorComputer at yahoogroups.com, "Paul T.

> Barton" <idezilla at y...>

> wrote:

> > 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

> ********

> 

> 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. 

> 

> james

--snipped--



		
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