RE: Batteries (was Re: LZ: Security my ass)


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RE: Batteries (was Re: LZ: Security my ass)



BTW, I pressed on one with the 4 AAAs out and the lithium in, then immediately 
realized what I had done and crammed some batteries in. My memory was fine. 
The TI-85 must've detected that there wasn't much power when it came back on 
so it shut off.
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-----Original Message-----
From:	owner-list-zshell@lists.ticalc.org  On Behalf Of Mel Tsai
Sent:	Thursday, June 05, 1997 9:57 AM
To:	list-zshell@lists.ticalc.org
Subject:	Re: Batteries (was Re: LZ: Security my ass)

>>  I don't know how correct this is, but here's my reasoning: The lithium
>> battery _does_ work. When the calc is turned off, you can pull all 4 AAAs
>> out, leave em out (I've done this overnight cause I needed to recharge my
>> AAAs) and put em back in later. As long as the calc remains off, the
>> lithium battery keeps your memory intact. I think something happens that
>> switches power useage over to the lithium when you turn the calc off. (Any
>> one tried pulling the batteries after a powerdown from within ZShell?) But
>> if the calc is on and you pull the batteries, you distrupt the circuit and
>> the calc doesn't have a chance to switch power sources.
>> If anyone can confirm this, let me know.

Pulling out the 4 AAA batteries after powerdown and then pressing "ON"
will reset your calculator no matter what.

Pulling out the batteries when the calculator is already on is a
different story.  The "switching circuit" you're referring to is
probably a diode/capacitor detector circuit.  When the main power gets
below a certain threshold (probably 3.2-3.6V) the main supply diode
becomes reversed biased and the lithium takes over.  If the lithium
isn't present then the other diode becomes forward again, so you
always have battery retention with at least one power source.  This is
probably cross-linked to some other circuit (probably the "on" switch)
that also controls the power, and this is why pressing "ON" can reset
the calculator when the main batteries are out.

For more information on such mechanisms visit the dallas semiconductor
site.  They have all sorts of discrete IC power controller/memory
backup chips that may also explain how the TI-85's power works.

-Mel
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The TI-Memory Expansion Homepage
-http://www.egr.msu.edu/~tsaimelv/expander.htm


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