PDP-8 /e/f/m memory

Allison ajp166 at bellatlantic.net
Tue Aug 15 07:26:29 CDT 2006

>Subject: Re: PDP-8 /e/f/m memory
>   From: "Chuck Guzis" <cclist at sydex.com>
>   Date: Mon, 14 Aug 2006 22:19:08 -0700
>     To: cctalk at classiccmp.org
>On 8/14/2006 at 9:35 PM Don wrote:
>>Unless you can make a battery application last A VERY LONG TIME
>>(not just a LONG time since those are the cases where you get
>>screwed because you have forgotten about the battery that
>>you replaced 1 or 2 years ago... *but*, if you replaced it
>>*10* years ago you don't mind -- as much -- when it dies
>>after that long of a service life) it will frustrate users.
>Well, consider the Dallas battery-inside-the-chip clock-calendar circuits.
>7 years sounded like forever--and it may well have been to the original
>owners of the equipment.  But now, they're starting to fade and finding
>replacements can be a bit of a hassle.  In 20 years, it'll probably be
>nearly impossible.

I shave off the top of the DS1287s and replace the cell.  It's easy to find
the battery on those as it's magnetic!

>For this particular application, any keep-alive power source needs only to
>last as long the longest power-off interval.  If, as Don, says a supercap
>will last several months, that should be good enough--and it's a permanent
>solution.  Heck, I wonder if you could trickle-charge the battery with
>ambient light via a solar cell.    That should extend the keep-alive period
>I just don't like chemical reactions in my equipment--it's sort of like
>bird's nest soup.  It might taste good, but I don't like the idea of eating
>bird spit..

Then place the battery at the ends of two wires remote from where their 
failure can do harm.   

Experience is a good adaquately sized Li cell is by far the easiest solution
when used with the Dallas ram controller chips.   


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