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From: scotty@l5comp.UUCP (Scott Turner)
Newsgroups: comp.sys.amiga
Subject: Re: 14.31818 MHz 68010 Upgrade
Message-ID: <327@l5comp.UUCP>
Date: Mon, 17-Aug-87 05:26:31 EDT
Article-I.D.: l5comp.327
Posted: Mon Aug 17 05:26:31 1987
Date-Received: Wed, 19-Aug-87 04:40:21 EDT
References: <19965@ucbvax.BERKELEY.EDU> <204@dana.UUCP>
Reply-To: scotty@l5comp.UUCP (Scott Turner)
Organization: L5 Computing, Edmonds, WA
Lines: 44
Summary: DRAMs refresh and you.

In article <8708111710.AA12671@cogsci.berkeley.edu> bryce@COGSCI.BERKELEY.EDU (Bryce Nesbitt) writes:
>>In the marjority of cases it is better
>>to blow alternate cyccles for hidden refresh than to use a contention
>>refresh scheme that causes wait states...

Yeah but just make sure you don't blow EVERY alternate cycle for refresh! You
only need a refresh cycle every 15us... In fact the number 28 works out real
slick on a 7.14MHz Amiga as the number of memory cycles to skip before using
an alternate cycle for a refresh, or stealing a processor cycle.

>BTW1: Dynamic ram can take a *long* time to decay.  On the order of multiple
>seconds.  Not that this information is of any use -> I'm sure a refresh
>system built on this as fact would be quite doomed.

Actually the ol' 16Kx1 DRAMs could take 10 to 15 seconds to decay at room
temp. I wrote this program to load the ram then cease activity till I told
it to scan the ram and check it to see if any bits had decayed. I had to do
it that way because of course the act of reading all the ram would refresh
it! :) I then turned off the refresh and played with it. I found that if it
cooled the board down with freeze mist I could make those suckers hold their
values for over a minute! Hit it with the heat gun and none would last more
than 4 seconds.

But as chips got denser and denser the capacitors got smaller and
smaller...  The current 256Kx1's and 1Mx1's can't perform these herculean
refresh feats.

>calculation.  I had a lot of fun with this-> but I never go byond using a
>paper mask to create test images.  I didn't and don't have a lens set up of
>any type.

I'll give ya a hint Bryce, Micron Technology. Not only do these guys make
DRAMs with clear lids they even have lenses. ;)

One point Bryce didn't touch on, if any of yall were going to play with yer
DRAM's, is that once you take that lid off the chip is EXPOSED. This is OK
for fooling around but for longer periods of time the chip will breakdown.
(This is why Micron Technology puts a clear lid on their OptiRAMs)

Scott Turner
-- 
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GEnie: JST			 | "The bombs drop in 5 minutes" R. Reagan
		"Pirated software? Just say *NO*!" S. Turner