[sdiy] How to use DRAM ?

[Jim Patchell]

    It has been a long time since I have done anything with DRAMs.  They
are not exactly the easiest things to use, and the newer ones might work
differently than the ones I designed with (last time I used a DRAM,
state of the art was 256Kx1 !).

    The biggest pain in the neck is dealing with refreshing, the second
biggest pain in the neck is dealing with the address multiplexor, which,
really, is the same problem.  Some of the newer (well, 15 years ago or
so) DRAMs have interenal refresh counters, which make the refresh job a
little easier.

    To access a DRAM, you first stobe in the row address (RAS) and then
the collumn address (CAS).  The R/W line controls reading a writing.
Timing of these signals is critical.  There are many different ways to
do it.  I have some old motorolla app sheets for interfacing DRAMs to
68000's, but the idea is applicable for any application.  However, these
app notes are for the older DRAMs, I do not know if any or how much
would apply to the newer parts.

    Tonight, I will pick an app note, scan it in, and post it on a web
site.  If nothing else, you may find out just what you are getting
yourself into.

    My personal thoughts.....stick with Static Rams.  Yeah, they are
easy to use, but not as Manly as a DRAM.  Static Rams are for wimps and
bed wetters.

    -Jim

Michael Buchstaller wrote:

> as most other people, i have some 30- and 72-pin PC Memory
> modules lying around. (4 MB...32 MB each)
>
> Modern mainboards all wants DIMM´s, and everybody is throwing
> out old 486 and early pentiums with such SIMM memory in them.
>
> My idea is to use them in a sampling module or maybe a digital
> delay.
> But how does one access this RAM ? I have done simple things with
> SRAM´s, but if i remember correctly, DRAM´s need some sort of
> refreshing, and have to be re-written after reading.
> How does one do this ? Has anybody used DRAM´s in a project
> successfully? (without special SMD memory controllers of course)
>
> -Michael Buchstaller