Calculator blog

Musings and comments about our common interest


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Even more memory in a HP15c LE?

For those of you that have a HP15c LE, and remembering the previous post about cabling to repurpose a 12c to a 15c - now there is something that can be interesting to you!

The forum thread is here:

At the beginning of the post (already cited in the previous blog installment), they discuss the different HP15c firmware available, and they post three of them.

But later in the thread, there is a discussion on how to increase calculator memory in firmware, by patching the original ROM that is in every HP15c. The ROM adressed the available memory of the original calculator, but in the emulated system there is more memory! So there have been several attempts at increasing the memory by patching the original ROM in selected places.Someone has reached 128 registers (the original machine has 64), and there is an in-depth discussion on how to reach 192 registers. J-F Garnier even posts the ROM positions that need to be patched. 

With that information, we have been able to create a patched ROM that allows for 192 registers. The firmware by default offers 94 registers and 99 non-allocated registers for programs and matrices. With this split, you could use 693 program steps. This is a screenshot of the MEM command, showing the above memory scheme. However, other splits are possible.




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Reprogramming a HP12c into an HP15c

There is still a lot of demand worldwide for the HP15c calculator. While the HP42 was arguably a better calculator, the sheer elegance of the HP15c beats it every time. All keys had three functions - at least, since some key labels could be understood differently if you were working with numbers or matrices (yCx and yPx), or as matrices or program labels (A to E keys). 

Si ti is no surprise that people want to get hold of an HP15c "on the cheap". the easiest way is to reprogram a current ARM-based HP12c. There was a recent discussion in on hp15c firmware for the old Hp15c LE edition issued in 2011 - and it was posted there ( I will not do it here due to copyright issues - at the end this is a business and it is better to stay safe)

To do it you need a cable to connect your computer with a JTAG connector like the one in the back of the calculator. these connectors are made of POGO pins, and are increasinglt rare:


It is the 6-pin connector in the middle. This is a recent HP12c calculator. Beware with the cable: there are two types of HP12c ARM-based. The ones prior to 2015 were based on an Atmel AT91SAM7L128 and the communication protocol is serial RS232; while after that there was a new model based on another chipset, the Atmel AT91SAM4LC2CA, and here the connection is USB !! (with the same outward connection)

I enclose here a screenshot of discussion about the pinout of the two calculators:
















You can get there more information on how to get the cable. Good luck!

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Register arithmetic on the HP15c

There had been register arithmetic features in other HP calculators before, but never with the depth and variety of the HP15c. We’ll see it in a moment.

What do we mean for register arithmetic? Let’s see how you would work with the contents of a register. Say that you want go get the contents of a register and add them to the X register. Without register arithmetic, you would need to call the contents of the register to X (RCL 5, for example), and then press “+” (by doing this, you would have raised the old X to Y, the old Y to Z, the old Z to T, and the old T would be lost – something to take care about when programming)

With register arithmetic, you would just do RCL + 5, and while the number of keys is the same, you don’t loss the T register! 

I may agree that RCL + (or -, x or /) are interesting but nothing to write home about. However, you can do the same with STO: add the X contents to a register. This really saves strokes, and it is much more elegant: compare:




with register arithmetic:

STO + 5

It also makes for shorter programs. Be careful with the division and subtraction operations: you need to remember that the second operand is always the one in the X register.

There are other interesting operations, involving the I register: you can operate with the contents of the I register, (STO + I), or with the contents of the register adressed by the content of I: STO + (I). These are very useful when programming – really clarifying the program flow

(Not related to register arithmetic, but worthy to discuss here too, is the exchange of X with the contents of a register: either a direct number (0 to 9, .0 to .9), the I register, or the register indicated by the contents of register (I): you use the key X »«)

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HP15c book

image0As the HP41 repair book has already passed the 500 units sold mark, I have been challenged to write a book on the HP15c.

Many years ago, there was a book called "An Easy Course in Programming the Hp-11C and Hp-15C (Easy Course Series)", by Ted Wadman and Chris Coffin, which I have not been able to get hold of. Then you have the fantastic user manual and also the Advanced functions manual - in itself a computer science crash course. Then there are many sites that have several programs, but nothing like a common respository with all known applications.

I am not the only one to love the HP15c. Its compact form factor, the ability to use it with both hands for a faster keying in, the complete and consistent fucntion set, the good memory sze for its time, made it a formidable calculator for the engineer and scientist calculation, when he was far from a computer. I still use it every day and the search statistrics of my site still show it as the most searched item - after all these years.

The manual will describe the machine, list its several versions, explain how its firmware can be upgraded, and will list many programs for all areas of scientific knowledge and for all educational levels. Most of the information is already available if you know how to search for it, but I have missed a place where you can read all of it with a consistent writing and enough explanations on what each program is doing.

You may say that it does not make sense to write a book about a discontinued calculator, but I know for a fact that there are many of them still in use around the world, with peaople searching for software and longing to read more about it.

Besides, I do not lose the hope of having it produced again...

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More HP15c

image0I am having a discussion with my son, an engineering freshman. He's just finished the first year, and he's very happy and thankful of having the HP Prime calculator. Probably it is the best calculator for a student nowadays. I have the feeling that the HP50g is the better calculator, due to its more "elegant" programming model; however, the Prime has more raw power and is easier to program is a procedural language similar to basic. (It is surprising what can be done with this language. You can take a look at the games that have been programmed with it in I hope that my children never see it or there goeas another distraction more)

My discussion with him versed on the fact that the HP15c is the best calculator to master "for the rest of his life". I see no point in having him using a HP41, even the cel: is a cumbersome machine that will occupy a lot of room in wherever he puts his things; The hp42s would be an alternative, but even that one is a little too big; but the HP15c is exactly the right size and has everything the prospective engineer needs - short of anything a computer spreadsheet or Mathematica or Mathlab can do. Plus, it is small enough to be really portable and carry it on your jacket pocket; and it keeps the utter elegance of the HP50g we were discussing about. 

I plan to have him learn how it really works. He'll have one as heritage, and he'll be thanking me for it in the long run. I guess that the Prime will not see much use after he has finished college!

I will give it to him with the leather case to increase the acceptance rate - by the way!

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This week I have been using the HP15c in my normal work. for that I have entered several financial programs including the Time Value of Money program. It is a long program but it makes use of many of the programming techniques in the HP15c.

The HP15c always surprises me regarding how cleverly distributed the keyboard is, and how well thought out is the function set. Most of the functions can be applied to complex arguments; also, compared with other HP calculators (including the advantage pack for the HP41c), the complex mode doubles the RPN stack and so programs can be applied to real or complex numbers, depending on which mode the calculator is; it allows to redefine the upper 5 keys; and you can combine complex numbers with the integrate and solver features.

A surprising capability on a calculator this size is the extended use of matrixes - you can invert matrixes and can also use them to solve linear systems - which is something you can do in an exam whithout anyone noticing that you're using your calculator. Also I liked how elegant is to solve an equation system: after entering the 3 matrix dimensions (coefficients, independent terms and results), you enter the values for each term in the matrix, and then you recall the independent term vector, you recall the coefficient matrix, and then you just press the divide key! then you have the result in the results matrix. So powerful, and yet so simple and elegant.

The calculator came initially with two manuals: one was the user manual, roughly equivalent to that of the other calculators (but with many more functions, of course); however, this was a machine devoted to scientists and engineers, and it should explain them with details how it works and what are the limits of operation and accuracy in the different functions and features. So, the machine came with an "Advanced Functions Handbook", pictured besides. 

The manual dealt with the following topics (reading from the index):

  • Using Solve effectively
  • Working with integrals
  • Calculating in complex mode
  • Using Matrix Operations
  • Accuracy of numerical operations

These subjects are dealt with detail and combining precision and clarity - a must read for any computer science student!

The previous anniversary version did not have this manual, only the User Manual. Let's hope that, if this calculator is ever resurrected, it comes with this manual too!


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I have created a "HP15c Corner" in our website. Something tells me that it will be useful some time soon. For the time being, we will put there all the HP15c or HP15c LE that we get for sale, and all parts and accessories related to them, including leather cases, battery covers, etc.

We'll also take care of the links to this wonderful calculator that we may find, as well as all the software for it that was available at the time.


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HP1CL is over!

tall_keys_-_5We have sold the last unit of HP41CL. So far there are no more made and no more planned - and it will be difficult to produce more since there are many parts that are out-of -life. The board would require a deep redesign which current demand does not warrant - so it is a pity for all of us!!

One of the last units sold was a 1937A serial number unit - one of the very first. I have only seen an earlier unit, a 1932A. It is a nice closing to the story, 43 years after its inception in 1979. I was there then and I remember the lust for that powerful machine, far from me as primary student. My father bought instead a HP33c for me - which hooked me into RPN - a hook that I have not been able to unleash so far.

With the so-far demise of the HP35s, there are now the HP12C, the HP12C platinum (which has an RPN mode), the HP17bII+ and the Prime as RPN machines. So far in Europe the HP12C has been absent for some time, but I have been promised that it is returned - so far that I have been able to place an order for them. I expect the order to arrive before month end.

We are missing a RPN scientific (not graphical), preferably of small size, not competing with bigger student units. I have been given hope by the current calculator management - let's see!


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Wsih list for Moravia-Royal

Now that the calculator business is in the hands of Royanl and Moravia, let's see what could be our wishist, now that the HP35s has been discontinued. A customer called me on Friday, and he told me "I want a RPN scientific calculator" - then I realized that there is no scientific RPN calculator anymore!!!

Rumours are that the HP12c will be put again in production (despite being in some dealers' inventories, it has been discontinued for at least 4-5 years). This would open the door for other Voyagers calculators - and I am thinking about my long time love - the HP15c - again.

Among the units in production we have the HP17bII+ - which is an excellent product and the most powerful current financial calculator. However, it has the same body and key disposition of the HP42s - so that is another possibility for a scientific calculator (the HP42s has not been bettered in my opinion) - with limited development time (both models could eventually be run on emulation layers with the original firmware)

However, the calculator market is based on school needs. These are best covered with the 300s+ and 10s+, and then with the Prime as graphical calculator (which runs circles around most of the competition).

I will try to send these thoughts to Moravia, who has been for some years my distributor.

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The original HP15C: the best HP product ever?

This week we have sold an original HP15c in bos, and in pristine shape. While I was reviewing its compact box, the instructive manual and the machine itself, I kept thinking that it was the best hp product ever.

Capable of inverting an 8x8 matrix, solving equation systems with complex numbers, and having all keys with three different functions (and in some cases 4), it has the most elegant logic of all units I have seen. Nothing is superfluous, nothing repeated, everything has a purpose. And it is compact and beautiful - the ideal lab calculator. 

Here are some pictures of it:




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