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From: ftpam1@acad3.alaska.edu (MUNTS PHILLIP A)
Newsgroups: sci.electronics
Subject: Re: Dallas Semi Intelligent Sockets?
Message-ID: <1991Jan28.083000.28601@ims.alaska.edu>
Date: 28 Jan 91 08:30:00 GMT
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In article <3222@naucse.cse.nau.edu>, rrw@naucse.cse.nau.edu (Robert Wier) writes...

[query concerning Dallas NVRAM's and SmartSockets delete]

> I'd be interested in hearing from anyone who has knowledge about
> or has used these, price range, etc...

     I have worked with the NVRAM's from Dallas Semiconductor (and Thomson-CSF
also).  Prices for small quantities are in the $20.00 range, depending on
density and speed.  The SmartSockets are cheaper, but you have to add in the
cost of the RAM.  Dallas Semiconductor devices can be ordered by credit card
for overnight delivery at 1-800-336-6933.  Product info may be requested
from 1-214-450-0969.

     All of these devices (and EEPROM's as well) share a common problem:  the
microprocessor accessing them can go berzerk on power-up and especially power-
down conditions.  I have even seen this with serial EEPROM's that have an
extremely complicated access protocol.  The Motorola 68HC11 single chip
microcomputer with internal EEPROM also suffers from this problem.

     The only solution is to make sure the microprocessor is reset whenever
its supply voltage is out of tolerance.  This requires special low voltage
detectors; circuits based on op amps or comparators and Zener diodes are not
accurate enough.  They company I worked for at the time was unwilling to pay
for the low voltage detectors and they have suffered from product unreliability
to this day.  (I still do software for them on a contract basis.)  I liked the
5 terminal regulators that SGS and now National Semiconductor make; the low
voltage detector is on the same die as the regulator so everything should track
with temperature, etc.  These regulators have a pin for a capacitor and a pin
to reset the micro whenever the output voltage is out of tolerance.

     My prediction is you will need to retro fit this sort of protection
circuit into your system if you intend to use NVRAM's or SmartSockets.

Philip Munts N7AHL
NRA Extremist, etc.
University of Alaska, Fairbanks