[sdiy] How to use DRAM ?

[sasami at blaze.net.au]

There is one very obvious way to use old PC memory for delay 
lines. That is to use the PC motherboard to manage it. Any 
486 era machine will have more than enough grunt to do the 
job, and later machines even more so. With a bit of clever 
programming, the A/D functions could even be handled by the 
processor using successive approximation. You will of course 
need to wire up an interface.

Ken

>    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