From: Ojala Pasi 'Albert' (albert_at_cs.tut.fi)
Date: 2003-06-13 08:44:42
> RAM is build from Flip-Flops (FF), which have two states: 1 and 0 (or: on and
> off). Well, this is not really true with the C64's RAM, because it is DRAM
> (and not SRAM), but the effect is the same.
DRAM is made of capacitors, and SRAM from flip-flops. SRAM is more stable
even when you cut the power (unless you are in .18-micron with high
transistor leakage currents). Capacitors on the other hand always leak
their current away unless you are constantly (peridiocally) reloading
them (DRAM refresh).
> What can be remarked is (at least in every situation I have worked with
> RAMs) that they tend to generate a 1-0-1-0 pattern, i.e., "neighbored"
> addresses are most likely to have opposite states.
This is because the neighboring cells usually have different polarities.
The cell itself 'resets' to the same state, but the column-read logic
inverts every other read line. This is so that when you have memory
contents of $ff or $00, interference between read lines (in reality
the read lines are differential) are minimized, because the cells
(capacitors in DRAM) have different contents.
For 1-bit DRAM's you get a $ff $00 -pattern, with 2/4/8-bit DRAM's you
might get a $aa $55 -pattern.
-Pasi
--
"When I marry, I want it to be for love."
"Ah, a radical?"
-- Vir and Lyndisty in Babylon 5:"Sic Transit Vir"
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