Xref: utzoo comp.misc:7420 sci.electronics:8692
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!swrinde!gem.mps.ohio-state.edu!uakari.primate.wisc.edu!xanth!lll-winken!scooter!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.misc,sci.electronics
Subject: Re: Non-volatile Memory--EEPROM
Summary: RAM with integral battery
Message-ID: <1836@neoucom.UUCP>
Date: 18 Nov 89 06:28:49 GMT
References: <1308@rodan.acs.syr.edu> <65243@psuecl.bitnet> <1230@corpane.UUCP> <2335@cbnewsj.ATT.COM>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 25



I noticed when I looked inside my AT&T CEO 2224 modem that it used
a RAM chip with internal battery for holding the setup information.
The nonvolitile RAM was about double the height of a typical J type
24 pin JDEC package.  It apparently has its own internal lithium
cell (which appears to be non replacable).

It has been a while since I had the modem apart, but I believe the
part was manufactured by Dallas Semiconductor.

Seems like a saw a write-up on the aforementioned parts in EDN or
a similar magazine a couple of years ago.  The battery RAM contains
a powerdown circuit to prevent blowing away the data when Vcc goes
down.  I recall from using a 5313 2K * 8 EEPROM from Seeq (old
technology now) that you had to be careful holding the write enable
line while power was applied so as to avoid zeroing the chip.

The number of writes on an EEPROM is several hundred thousand, so
one needn't worry too much unless considering using it for
scratchpad memory durring program execution.  One wouldn't want to
do that anyway, as the write time is pretty long.  The older parts
like the 5313 had write times on the order of a couple of mS!

Bill