On Tue, 21 Apr 1998 08:58:44 +0200 Werner Terreblanche
<wterreb@PLESSEY.COM> writes:
>I suppose it makes a lot of sense to
>investigate
>the ISD chips a little bit more closely.  The things that I need to
>find out
>about these chips are if their memories are non-volatile

Yes it is, they are EEPROM.  They claim 40 to 100 years data retention
and it seems that the chips (at least the ones with the parallel
interface) are well-protected against unintentional writing by tying the
R/W pin high.

and whether
>it is
>easy to make duplicates of pre-recorded chips for production
>purpouses.

It's not hard, but the normal recording mode must be used (meaning it
will take 20 seconds to duplicate a 20 second chip, etc.).  ISD offers a
"programmer" that makes duplicates or one could be easily built.  If you
need tens of thousands of duplicates the duplication may be a problem.
If that is your case, write or call ISD and ask them if they can supply
pre-programmed chips.  They may be willing to work with you if you are
dealing in large quantities.


>I once saw a Texas Instruments chip once which meets both these
>criteria.
>It's a one-time programmable chip which allows you to store a number
>of
>speech messages (128 seconds worth).  The disadvantage is that its one
>time
>programmable, but the advantage is that it's completely non-volatile.
>Decisions... decisions hey?  :)

I think the TI chips use a LPC algorithm to store a lot of speech in a
small memory, but with a very heavy "synthesizer" effect on the sound.
If this is the case, you'll need special software which TI may not give
you in order to encode your speech for programming.  But a large library
of common standard words should be available.

I was just looking at ISSI (www.issiusa.com).  They have some chips which
store ADPCM digitally in a OTP ROM.  The memory capacity isn't very large
(512K bit, samples are 4 bits so that's 16 seconds at 8K sampling) but I
think some of them had interfaces for external ROM.  I don't know if the
quality would be very good either since they seem to be targeted to very
cheap "squawking" devices using piezo speakers.  Everything about the
ISSI chips (how to encode, how to program) seems to be proprietary.


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