Differences between the HP 15c CE and the original HP-15C

[Gene]

The HP 15c CE Owner's Handbook describes all the major differences between the HP 15c CE and the original HP-15C. However, there are some additional minor differences, which arise from the complexities of making firmware written 40 years ago communicate across hardware from today. The danger of creating a problem by fixing what are really cosmetic issues was not deemed worth the risk. This is a more comprehensive list of all known differences.

Performance

The CPU of the HP 15c CE is more than 200 times faster than the CPU in the original HP-15C. Due to overhead, real-world performance does not increase by this much, but typical operations are 10–20 times faster than on the HP-15C.

If a program written for the original HP-15C relies on special timing, for example if the expected run-time of a program gives the user a fixed time to react, then that program will need to be slowed down on the HP 15c CE, possibly by the addition of [PSE] (pause) steps or by making loops repeat more times.

Memory

The HP 15c CE provides 50% more memory than the HP-15C — 672 bytes instead of 448 bytes. This increases the number of allocatable storage registers from 64 to 96.

This means the [g] [MEM] function, which displays the available registers and their allocation, will appear different due to the increased memory on the HP 15c CE. The default allocation shows “19 78 00-0” instead of “19 46 0-0”.

The original HP-15C was limited by memory to a maximum matrix size of 8 × 8. Despite the increased memory of the HP 15c CE, the limit of 8 × 8 remains for matrix inverse, determinant, and division.

Battery Usage

The greater performance means greater battery requirements, too. The HP 15c CE uses two lithium batteries instead of three alkaline or silver-oxide batteries in order to provide sufficient current.

The low-power indicator is designed to give you plenty of warning before the calculator stops functioning. The calculator does this by checking periodically after keystrokes to see whether the batteries will soon need replacement.

To minimize power consumption, the calculator normally operates in a low-power mode, with the processor running at a slow speed. When running user programs (including integration), the calculator switches the processor to full speed, which increases the demand on the batteries.

However, when the low battery indicator comes on, the calculator will only run at the slow speed to avoid overloading the batteries.

Most programs will complete in a second or less, often much less, and appear to be instantaneous. But if your program is designed to run for very long run times (i.e., exceeding 10 seconds), it is possible that before the low battery indicator comes on, you can deplete the batteries to below level that safely maintains memory, so some of your programs and/or data could be lost.

To avoid this, be sure to have new or relatively fresh batteries installed before executing user programs with extended run times. Note that this "difference" exists with similar products from other manufacturers.

Self-Tests

Because of the different hardware platform, the HP 15c CE has a different self-test system than the HP-15C had. This means the self-test operations provided on the original HP-15C no longer give valid results. The new self-test procedures are described in Appendix F of the Owner's Handbook.

Display

The original HP-15C had fixed display contrast. The contrast on the HP 15c CE can be adjusted by following the steps on page 63 of the Owner's Handbook.

The behavior of the flashing "running" display is also slightly different on the HP 15c CE. Sometimes the "running" text will flash at a different speed than on the original HP-15C. It may even not flash at all, for instance, during loops of complicated MATRIX instructions (50 repetitions of 8x8 determinants which takes about 20 seconds to run is one example), but given the processor speed of the HP 15c CE, this is unlikely to be noticed with any user program. It does not affect any computational results.

Key handling during “temporary displays” is different on the HP 15c CE. Temporary displays are when you press [g] [MEM] to temporarily display the memory allocation, when you press [f] [PREFIX] to temporarily display the full mantissa, or when, in complex mode, you press [f] [(i)] to temporarily display the imaginary component. In these three cases, while the temporary display is up, key presses are accepted on the HP 15c CE rather than ignored as they were on the original HP-15C. If you press a single digit key, the digit you pressed will be displayed and flashing. Pressing any additional key will stop the flashing. Since this behavior is not intended on the original HP-15C, the best way to avoid this difference is not to press a key during a temporary display of course.

Synthetics

"Synthetics" on the HP-15C original fall into what PPC termed NOMAS (Not Manufacturer Supported) and were never core functionality in any way described in the original manual. As mentioned below, they were a "trick" - an unsupported one - and those tricks are not present in the HP-15C CE.

[Rolief_Rechner]

Thank you for this informative post!
Looking forward to the arrival of one I ordered.

[ThomasF]

Hi Gene!

Thanks for a great comparison between the two calculators!

How is it with "synthetics" on the CE? This is (obviously) not mentioned in the Owner's Handbook ...
Will it behave as the original calculator, or is this door into the internals lost in the new one (I assume it is)?
If so, maybe we have to find a new passage into the machine ...

https://literature.hpcalc.org/community/...hetics.pdf

I.e. does the "rotate" function work on the CE?
* Enter "12345" into X (don't press enter)
* Turn off
* Press "Y^X" while turning on
* Press f PREFIX --> Display will show "00010048P1" if rotate works

This works fine on my original HP-15C, and also e.g. on the go15c app for Android

Cheers,
Thomas

[Divasson]

Hi,

I have one HP15c CE and one HP15c "old" in front of me, and the old does the rotation trick while the other does not (just shows 12345,0000 as "completed entry")

[Gene]

Couple of additional notes that I will add to the top post.

This list is not "my" list. Much of it is in the actual HP-15C CE manual itself and several people here helped with reviewing the write-up of this list.

"Synthetics" on the HP-15C original fall into what PPC termed NOMAS (Not Manufacturer Supported) and were never core functionality in any way described in the original manual. As Jose called them, they were a "trick" and that trick is not present in the HP-15C CE.

And FYI - one of the longer running programs for the HP-15C, Valentin's e to 208 places, takes about 20.5 seconds with the PSE instruction removed on the HP-15C CE.

[ThomasF]

(06-12-2023 06:00 PM)Gene Wrote:  "Synthetics" on the HP-15C original fall into what PPC termed NOMAS (Not Manufacturer Supported) and were never core functionality in any way described in the original manual.

Yes, thats why I wrote "obviously" regarding the manual ...

Ok, so then we have to find a new way to "trick" the calculator to open up like we did in the old days!

Cheers,
Thomas

[KeithB]

That would be with the SPI/JTAG programming port.

[Gene]

(06-12-2023 06:48 PM)ThomasF Wrote:  

(06-12-2023 06:00 PM)Gene Wrote:  "Synthetics" on the HP-15C original fall into what PPC termed NOMAS (Not Manufacturer Supported) and were never core functionality in any way described in the original manual.

Yes, thats why I wrote "obviously" regarding the manual ...

Cheers,
Thomas

Gene: No worries. I wanted to make sure that late-comers to this thread wouldn't think something supported originally was missing :-)

[Valentin Albillo]

.
Hi, Gene & all, (my highlighting)

(06-12-2023 06:00 PM)Gene Wrote:  This list is not "my" list. Much of it is in the actual HP-15C CE manual itself and several people here helped with reviewing the write-up of this list.

I assumed that much but see below.

Quote:And FYI - one of the longer running programs for the HP-15C, Valentin's e to 208 places, takes about 20.5 seconds with the PSE instruction removed on the HP-15C CE.

Thanks for mentioning my HP-15C Multiprecision e program featured in my PDF article Long Live the HP-15C, much appreciated.

In the article, I mention that it takes my program 62 min. 43 sec. to compute e to 208 digits on a vintage HP-15C, but that timing includes the execution of 124 PSE (Pause) instructions specifically included for the user to see steady progress instead of staring at a blinking "running" display for an hour.

If we subtract those ~124" from the total 62' 43" we get 60' 39" = 3,639". But you then say that the new HP-15C CE takes just 20.5", which means it runs my program about 178x faster, which is inconsistent with your OP statement that says, I quote:

"The CPU of the HP 15c CE is more than 200 times faster than the CPU in the original HP-15C. [...] but typical operations are 10–20 times faster than on the HP-15C."

So, which is it ? More like 10-20x faster or more like ~178x faster ? I sure hope it's the latter value, else the faulty Limited Edition would be much faster, at 90-100x.

Last but not least, the available 672 bytes vs. the original 448 bytes means that my program (with a one-step change) would now be able to compute almost ~300 digits of e on the new CE instead of just about~200 digits.

Thanks and regards.
V.

[Gene]

The CPU is roughly 200x faster, but the final speed increase depends upon the mix of operations being executed (of course). Rather than promising all instructions will run at X times faster, the safer thing in the manual was to under promise.

The 178X faster than the original HP-15C is what I experience on your HP-15C Multiprecision e program.

Some operations are not much faster on the HP-15C CE than on the HP-15C LE, but some are faster.

For example, the N-queens problem found here on the museum site:

15C - 4750 seconds
15C LE - 28 seconds
15C CE - 25.5 seconds - 186 X faster than the original

The LBL A + GTO A loop run for 60 seconds

15C - 297
15C LE - 50,609
15C CE - 54,086 - 183X faster


but as I indicated earlier, not all functions show the same speed increases. At this year's HHC gathering, there will be a presentation on the speed of the various HP-15c incarnations.

[Valentin Albillo]

.
Hi, Gene, {my highlighting}

(06-13-2023 12:29 AM)Gene Wrote:  The CPU is roughly 200x faster, but the final speed increase depends upon the mix of operations being executed (of course).

Of course. That much is obvious.

Quote:Rather than promising all instructions will run at X times faster, the safer thing in the manual was to under promise.

First, no one should promise anything, the manual should just give true and useful factual information, not promises, under or overstated. A much proper statement would be, e.g.:

"The actual speed increase varies with the particular instruction or mix of instructions executed but typically will be ~10-20x for instructions executed from the keyboard, and ~170-180x for running programs."

Quote:Some operations are not much faster on the HP-15C CE than on the HP-15C LE, but some are faster.

Which ones ? Can you give some examples ? How much faster ?

Quote:For example, the N-queens problem found here on the museum site [...] 186 X faster than the original. The LBL A + GTO A loop run for 60 seconds [...] 183X faster. [...] your HP-15C Multiprecision e program [...] 178x faster,

Those three programs surely have very varied mixes of instructions. Mine, for instance, has a 42-instruction loop which includes matrix operations, tests, storage, arithmetic, branching, incrementing, the works, which is executed 124 times, thus more than 5.200 user instructions executed in all.

This surely allows a pretty good average on instructions' execution speeds, which comes out as 178x for my program, and similar values for your own two examples, and I feel it should be included as part of the 10-20x statement in your OP (and in the list you've based your OP on, and in the manual if it doesn't mention it. Not including it has the potential to unfairly belittle the HP-15C CE's speed capabilities.

A "promise" safety factor of 2.0 might be acceptable, but a safety factor of 8.0-9.0 is way too much.

Thanks and best regards.
V.

P.S.: My other possibly useful HP-15C programs for speed benchmarking purposes include:

Feigenbaum for the HP-15C (Message #4), 477 seconds for 7 iterations.
HP-15C Mini-challenge: My Original Solutions & Comments (Message #55), 444 GSB A takes ~7 min.
A physical HP-15C solution in 48 minutes (Message #13), ditto, it takes 48 min. to find the solution.