Speaking of DRAM what I can recommend you is to use RAM
with EEPROM build in it. every thing is inside when you power it on
it will automatically load data from eeprom when you turn it off
it will automatically load data to eeprom. I played with it it is
very good toy but it is more expensive.
if you need to try I can look for the name. I have a data book.

Andre

Danjel McGougan wrote:

> Hi all,
>
> First of all I want to thank everyone who answered my mail concerning
> audio compression algorithms. They were really helpful and now I have
> a general idea of how to proceed.
>
> For those of you who didn't read the mail: I'm thinking of building a
> digital telephone answering machine and needed some help in deciding
> what type of memory and software compression to use for storing the
> speech.
>
> I'm going the hard way without the use of ISD's chips. I'm
> thinking of using a 2M x 4 DRAM chip for storing 4-bit ADPCM codes at
> 6kHz sampling frequency. This gives me approximately 6 minutes of
> speech with reasonable quality which ought to be enough.
>
> I've written ADPCM decoding and encoding routines and found that I
> need about 110 program cycles per sample to encode and about 80
> program cycles to decode. With overhead I'll probably need a crystal
> running at 8MHz.
>
> Now to the problem. I need to use DRAM which I have very little
> experience in using (I'm really a software guy, not hardware). How
> does one proceed to design a battery backed-up system with a DRAM and
> a PIC processor? I understand that the DRAM must go into self-refresh
> mode when the power is cut. Also, how do I get the memory to refresh
> during normal operation? I understand that I probably need some kind
> of external counter and perhaps something else to run the refreshing.
> I'd really appreciate ideas and schematics for solving some of these
> problems or all of them :-)
>
> Thanks in advance,
> Danjel McGougan.



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