Every time I see one of those evil NiCad batteries, I replace it with
a 0.5F supercap.
I have never had an issue with my M100, or with the Olivetti
equivalent (number escapes me at the moment)
Having said that, the oldest would have been 8 years ago, so I don't
have the same 30years of experience regarding leaking characters.
Doug
On Sun, 17 Mar 2024, 11:44 am Brian K. White, <[email protected]>
wrote:
You can run plugged in to the wall for all normal random on/off
operating times without worrying about it too much, IE, all day
long for
8 to 12 hours or whatever, and for multiple days in a row, if
unplugged
when turned off.
And you can leave it plugged in turned on or off overnight for one
night
to a few days.
And you can even get away with exceeding those pretty badly once
in a while.
What you want to avoid is plugging it in and leaving it plugged in
24/7
for weeks or months or years, whether it's on or off.
The harm is the charging circuit that charges the internal nicd
battery
soldered on the motherboard. The battery is not a lead/acid or gel
cell
that has a float value where it can just stay floating at a certain
value forever, and the charging circuit is not a smart modern battery
manager that knows how to stop charging when the battery is full, it
just keeps on supplying a bit higher voltage than the the cells own
voltage, and current just keeps on flowing backwards through the
cell,
and sooner or later this kills the battery by a couple different
possible mechanisms from plain heat & pressure making it leak and
cook
off all the electrolyte, to things like the electrolysis process like
electroplating, eating away all of one plate and building gunk up
on the
other.
It's pretty forgiving so you don't have to be super careful. You can
*mostly* never even think about it, and a normal random usage pattern
will just naturally be fine. Just don't plug it in and forget
about it
for a year.
It doesn't touch the AA's and it doesn't matter if the machine is
turned
on or turned off.
Now that you make me run through it all like that, I realise this
might
finally be be an actual valid useful reason to install a supercap
instead of a new nimh cell.
Mostly there is no point, because both a cap and a battery will only
last about the same number of years, and both will start to leak
corrosive juice after about the same number of years. A cap is not
harmed by being allowed to go all the way dead (which a battery
is), nor
by being allowed to stay dead for a long time (extra especially
bad for
a battery), but even a battery that has been so badly treated still
supplies more standby time than a brand new perfect cap. All in
all, no
point.
But one difference that matters, a cap should not be harmed by the
crudeness of the charging circuit. A cap will just charge up and stop
conducting and won't care about the charging supply at all. No
current
will keep flowing through the cap, no cooking or electrolysis etc.
I have always been very much not in the supercap camp, but this is
one
real thing.
--
bkw
On 3/16/24 16:33, Will Senn wrote:
> Wow, Brian! Super clear. Now, I want a REX# :).
>
> When you say that leaving it plugged in will kill the battery,
do you
> mean that I should run it off AA batteries most of the time and
not my
> 6v 200ma adapter? And the battery you're talking about killing
is the
> nicad on the board, right?
>
> Thanks,
>
> Will
>
>
> On 3/16/24 3:21 PM, Brian K. White wrote:
>> I summarize REX as: "An on-board software-controlled option rom
>> library and ram image library."
>>
>> That's the shortest way I've found to say what it does, but
that's not
>> the same as saying what it's good for or why you want one.
>>
>> Because of the particular features and limitations of a M100,
probably
>> the single most life-improving thing you can do to one is to have
>> TS-DOS in ROM.
>>
>> That one thing addresses a few different pain points.
>>
>> The biggest pain points of a M100 are:
>>
>> - Battery-backed ram only storage. Very little storage, and easily
>> erased or corrupted, either by dead batteries or a software crash.
>>
>> - The way in manages machine-language software. How they all
want to
>> run in the same place in ram, yet the OS does not provide very
much in
>> the way of automatically moving programs into and out of that
spot, so
>> software is always clobbering other software, or you limit
yourself to
>> just having a single machine language app installed, or you
have to
>> figure out the arcane way to hack the binaries to relocate them
to run
>> at different addresses side by side, or you have to keep double
copies
>> of binaries so that the running copy can get clobbered and later
>> replaced from the ram file copy...
>>
>> - The main rom provides no binary file transfer other than the
>> cassette. And no *convenient* file transfer even for text.
>>
>> These things combine to make life kind of difficult. For
instance you
>> want some better file transfer app, but since you have no
binary file
>> transfer to begin with getting the file transfer app itself
installed
>> is a pain. Then once it's installed, it consumes precious ram,
and is
>> easily broken because of the way machine language apps are are
run,
>> and the simplest way to address that is to have a 2nd physical
copy in
>> ram, which uses up yet more of that precious 32k. etc.
>>
>> Having any tpdd client at all installed in any form makes
transferring
>> files a breeze, including binary files. This somewhat
alleviates the
>> small ram problem because you can easily put files away and get
them
>> back, as long as your tpdd software stays working.
>>
>> Even better is having a full featured tpdd client like ts-dos
instead
>> of teeny, and having it in rom instead of ram.
>>
>> That alleviates all kinds of annoyances.
>> - It consumes almost no ram.
>> - It doesn't require a pain in the neck bootstrap/loader
process to
>> get installed.
>> - It isn't subject to being clobbered and needing to be
reinstalled
>> because of some other software writing over it or crashing.
>> - It isn't lost after a hard reset or dead batteries.
>>
>> With TS-DOS in rom, you can pick up a totally dead machine, or
totally
>> kill your machine with a hard reset on purpose, or suffer a
total ram
>> corruption from buggy software, and with just "CALL 63012" you
are up
>> and running again, connect to a computer and pull down files.
>>
>> But even though this makes a lot of things a lot better, this
still
>> needs a computer and serial cable. The tpdd client just makes
it so
>> that you can effortlessly connect to a pc and move files back &
forth,
>> and having it in rom just means you can effortlessly always
have the
>> tpdd client regardless of crashes or dead batteries.
>>
>> That still leaves a couple things that could be better:
>> - If you had a plain ts-dos option rom, it means you can't use any
>> other option rom because the single socket is occupied already
by ts-dos.
>> - You still need a serial cable and pc (or a real tpdd drive or a
>> Backpack or PDDuino) to actually get the files from somewhere /
put
>> them somewhere.
>>
>> REX gives you ts-dos in rom just for starters. It gives you
ts-dos in
>> rom which just that right there alleviates several things
above, but
>> also:
>>
>> - all other options roms besides ts-dos
>> - full ram image backups
>> - all on-device self-contained with no computer or serial cable
needed
>> (after initial loading)
>> - impervious to dead batteries or resets or crashes
>>
>> And although you do need a computer to install option rom
images onto
>> the rex one time, ts-dos in particular is pre-installed, so that
>> single most-needed one never needs even the initial one-time
install
>> from a computer. Only all the other roms need to be loaded from
a pc
>> once. And the loading process is easy, because REXMGR uses tpdd
>> protocol internally to pull the rom images from a pc. No
>> bootstrapper/loader procedure.
>>
>> The other option roms give you mostly a few different office
software
>> kits, ie spreadsheets and word processors, and a few other
things like
>> there is a FORTH rom and an assembler/debugger/renumberer.
>>
>> The ram image backups give you essentially more copies of 32k
ram. It
>> helps a few different ways:
>> - you can physically hold more than 32k of apps or data.
>> - you can recover from a dead battery or reset or corrupted ram
from
>> crashed software by restoring a ram image.
>>
>> There are something like 30 or so available slots, and each
slot can
>> be either an option rom or a ram image. That's a lot.
>>
>> All without a computer. In the coffee shop, on the train etc, just
>> recover from dead zero in a few seconds. Just "Call 63012" and
away
>> you go, all interactive app and menu driven after that.
>>
>> So that is why you want a REX of any stripe, REX Classic, REX#, or
>> REXCPM.
>>
>> Now for REXCPM in particular....
>>
>> Those particular advantages are something the REXCPM is less
good for.
>>
>> REXCPM does give you all of that, but only as long as the M100
>> internal battery is not dead and the REXCPM and bus adapter board
>> remain installed in both sockets.
>>
>> You can recover from software crashes that scramble the ram,
and from
>> intentional hard resets that wipe all ram (ctrl-break-reset),
but not
>> from dead batteries or switching off the memory power switch on
the
>> bottom for more than a few minutes, or removing the device from
the
>> m100 for more than a few minutes.
>>
>> If the M100 internal battery runs out, or you uninstall it for
more
>> than a few minutes (you do get a pretty good grace period of
several
>> minutes, maybe even over 10 minutes) then you have to reload the
>> REXCPM from scratch as you just experienced. If you had a REX
Classic
>> or REX# instead of REXCPM, all you would have done is type "call
>> 63012" and you'd be all back up & running. No pc, no "37 easy
steps".
>> Done. And to remember "call 63012" just write it on a sticker or
>> label-maker on the bottom. Put it on the underside of the
option rom
>> or battery cover if you want to hide it but then you have to at
least
>> remember that it's there.
>>
>> I did make a "UPS" for REXCPM that should keep it alive for a few
>> years, but it's pretty involved to build and ultimately hard to
justify.
>> I don't pretend it's practical for most people, but it does
work and
>> exists.
>> https://github.com/bkw777/REXCPM_UPS
>>
>> You have to buy the parts from digikey or mouser etc, order
pcbs from
>> elecrow or oshpark etc, and then it's a pretty fiddly soldering
job,
>> and it ends up costing as much or more than the rexcpm itself
just to
>> give it a battery. And for all that, I think I only estimated 6
months
>> per cell x 4 cells = 2 years, but that's after the M100's own
>> batteries run out, and if you have fresh alkaline AA's and a
charged
>> internal battery, the M100 itself can last anywhere from a few
months
>> to a year. So maybe up to 3 years?
>>
>> A better long-term solution would be a keeper. You remove the
rexcpm
>> and plug it in to something with socket and a big battery. But
that
>> doesn't help with one that's installed in a machine. You'd need to
>> remove it from the machine to put it in the keeper. Plus the molex
>> sockets are no longer made. There are a few around available
still but
>> this would be a wasteful way to use one up instead of keeping
them to
>> repair machines. Really, for the long term like over 5 years, it's
>> probably more practical to just let it die and reload it. With a
>> convenient bootstrapper and tpdd server on a pc, it only takes
a few
>> minutes to reload a rexcpm from scratch. It's several steps that
>> requires a cheat sheet to follow, but none are very difficult
or long.
>> The hard part is just deciphering the original directions to
figure
>> out what actually are the steps you need to do.
>>
>> So all in all, I'm not sure how necessary the ups is. It's
probably
>> more practical to just do 2 things to live a happy life with a
REXCPM:
>>
>> 1 - Keep it installed in a machine. And keep that machine charged.
>> (Unfortunately, you can't just lave the machine plugged in to
the wall
>> 24/7 for months, that will cook the internal battery.)
>>
>> 2 - Get good at reinstalling it. It's several steps, but it's
possible
>> to write a little cheat sheet that is easier to follow than the
full
>> original documentation. And none of the steps are very
difficult or
>> long. You don't even need the cheat sheet after a few runs through.
>>
>> If you aren't specifically wanting to run CP/M then I always say a
>> REX# is far more practical. REX# is an nvram device that acts
like a rom.
>>
>> Instead of ever needing to recover the REX, the REX is what
recovers
>> your M100.
>>
>
--
bkw
