Continuous memory


The 10-16C series calculators run almost forever on a set of batteries preserving the content of the memory.

However, it appears that my series 20 and 30 calculators use a charge, when turned off, in a few months time. Also the 41 appears very power hungry when turned off.

Is this normal?

Bo Kristoffersen


NiCds have a much shorter self-discharge time than the silver oxides used in the 10c series. With no load at all, a NiCd will typically be empty in a few months.

Alkalines have much longer shelf lives than NiCds but less than silver oxides. Most of my 41Cs run for years on a set of Alkalines but there are a few that have developed a fault that keeps them from powering down completely. These can run down the batteries in a month or so.

I've heard that due to environmental regulations (in the US at least), the new silver oxides won't last as long as the old ones but I haven't verified this myself.


I spoke to a guy here at work some time ago about the HP10-16 series (he has an HP11C). He worked in semi-conductor design in the US in the late 70's and was aware of the HP design. He still works with me so may be able to fill in the details (or correct my understanding of what he said) if anyone is interested.

He said the HP10-16 series used an unusual semiconductor process that had many features to reduce leakage current as HP went all out to improve battery life (leakage current is the current that drains the batteries when the calc is 'off'). He said that HP realized they had 'gone over the top' and had used a more standard (and cheaper) semiconductor process for later designs as this gave acceptable results and was much cheaper.

The above could explain why the pioneer series batteries don't last as long even when the same type of batteries are fitted.

While I agree that Dave's answer is true the above may be the reason why the battery life of the HP10-16 is better than any other electronic device I have come accross.


I read an article recently touting IBM's newest semiconductor advance-- silicon on insulator. Lots less leakage, therefore much more frugal with power "to run tomorrow's sophisticated lineup of handheld internet appliances"...

Seems they figured out a way of using silicon oxide-- itself an insulator-- as a physical interface to a glass chip substrate, so they can arrange the electron pathways in a more contained way, less stray fields, and so you can get better circuit densities and smaller features that work as well as the standard cmos processes.

But something was tugging at me while I was reading that... and I remembered that HP had been experimenting with silicon-oxide barriers in a modified cmos process, many years before. And they were doing it for one reason: saving microwatts.

I'm pretty sure that was their rationale; to isolate each gate so it didn't have the "leakdown" of typical cmos. Believe it was a bit LESS dense and more prone to manufacturing glitches than typical cmos; certainly it involved many more steps in fabrication, which meant it was more expensive and yields would naturally be lower without extraordinary care taken to assure good results. But HP at that time was one of the few companies that would go out on a limb for a new technology and MAKE it work. I believe the results were incorporated into the Saturn cpus.

Now, of course, IBM hasn't just reinvented the wheel, by any means; their contribution-- to lay a consistent uniform film of oxide down (in a vapor-deposition process) so that silicon and glass "stick" and meld where they wouldn't before... that's really cool, and totally NEW. And it calls for a sort of "inverted" topology of cmos gate structures too. We can look forward to lots of battery-powered fun in the future, stuff that runs on a AA or two and outruns your current Pentium-class coffee-warmers.

But it IS kind of a reminder of the trailblazer HP has been over the years, that they were grappling-- and solving-- problems for themselves (like power consumption) A QUARTER OF A CENTURY AGO that still hold significant technical promise today.

May HP/Agilent continue that legacy always.


I ran my HP-16C for something like 15 years on the original
set of batteries. It wasn't heavily used, but nevertheless
it was pretty amazing.

I remember one of the original C-MOS manufacturers coming
out with a new type of C-MOS called SOS (silicon on saphire)
in the late 70's I think. RCA also made the 1801 and 1802
static C-MOS CPU's which were used in space quite a bit.

They were static, so the clock could actually be stopped on
them. Single stepping through a program was done in
hardware! And, although nobody really recognizes it as
such, it's my belief that it was probably one of the first
RISC cpu's. (Every instruction ran in either one or one and
a half clocks I think, and they were extremely simple
instructions. Much simpler than most 8 bitters at the
time. And lots of registers compared with others.)

Not that this has anything to do with calculators...


You are absolutely right Bill. The RCA CDP 1802 and its brethren were neat chips-- made for RCA's space development unit at one time; eventually finding their way into toaster-ovens and dishwashers, as well as aboard satellites. Intersil still has the chip in their inventory list (!) at:

and I think (but can't be sure) that the "high-reliability" chip they mention is indeed the military "space-hardened" version of it that Sandia National Labs developed from RCA's IP.

Welllll.... if you could FIND a strict definition of RISC, the Cosmac chip isn't really it. But it IS darn simple and memory efficient; and that's enough for a lot of applications.

But believe it or not: MOST of the popular eight-bitters were static single-step capable; as long as you kept power to the chip itself, the "clock" could be 0 Hertz! This was easily true of the TTL chips (the Zilog 8400, old venerable "Z80", is a GREAT single-stepping TTL chip), but also designed to work on a lot of CMOS cpus as well. Look for the min clock spec = "DC" on datasheets.

The reason (well, one of them) was called "static testing". You tied lines high or low and stepped one clock cycle (pushed a button) to see that it did what you expected with those inputs. Handy in the days before in-circuit emulator pods and heavy-duty breakpoint-tracing facilities. Not so handy after dynamic ram and internal clock-doubling and other intervening cpu and peripheral features appeared.

If all this seems Way Off Topic, it is... (spank, spank)...

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