Casio FX-502P Geek


These pages were written as a bit of fun and to teach myself HTML. If you are the sort of person who, like me, can waste a lot of time playing with a calculator, you might just find it interesting. The topic of this site is the late 1970's/early 1980's Casio FX-502P, which was a top end programmable calculator. I believe it was the top of the range Casio calculator at the time. I've even read that it was the first LCD scientific calculator (1978). Please feel free to comment on or ask for corrections to this site by E-mailing me . You will find things on this site that you won't find elsewhere. (I wouldn't pretend that you couldn't live without any of it though!). If you're still using such old technology, you might just find the programs useful.

Click picture to enlarge On the left is my Casio FX-502P in its cassette adaptor, the FA-1, along with various bits of paraphernalia that came with either the FX-502P or the FA-1. The calculator has the programming overlay in place; this is why my calculator looks a bit different from other pictures on the web. (My overlay got stuck in place early in my ownership when I removed a backing to the overlay).In those days, Casio calculators came with instructions and conversion charts in both English and Spanish. You may see why I thought that the black on yellow would be a suitable colour scheme for these pages! Click image to enlarge (526kB) or here to see a legible version of the calculator itself (148kB).

Go to pictures and information on the FX-502P and associated calculators and assocessories.


Because of regular hits on this site looking for the manuals, I've added this section of Adobe Acrobat PDF files. In this section you'll also find the contents of the example cassette tape that came with the FA-1, which included music and games.

Go to PDF files of manuals and WAV files of the FA-1 cassette.

Free Programs

The programs on this site were all written by myself, unless otherwise stated, and are available for download. There is no charge and there are absolutely no guarantees for fitness for whatever purposes that you wish to put them. I believe that they all work and that any significant reservations are in the documentation. If you find them useful or interesting I would appreciate an E-mail.

Complex Number Program

The program that is supplied in the FX-501P/FX-502P program library for complex numbers is limited for interactive use. In the 80's I ended up buying a Sharp EL545 for its complex number capability only to discover that it was incapable of calculating a simple expression such as Z1/(Z2+Z3) without resort to re-inputting data! This gave me the impetus to write the progam you can download from this site. It also works on the FX-602P but would require trimming for the FX-501P/FX-601P. The program that I wrote has the following features: It is also a good example of the use of indirect addressing for both memories and GOTOs.

Go to the code and documentation for the complex number program.

Decimal to Fractions Converter Program

The program below was written to give the FX-502P the fractions functionality that my previous calculator, the Casio fx120, had had. I was a bit disappointed that the FX-502P didn't have fractions capability given that at the time I got the FX-502P it cost 75 when the fx120 cost 20. The program you can download below is basically a decimal to fraction converter. Obviously it is not 100% accurate but is does work with thirds etc. provided that the integer part is not too big. Be warned however that sometimes it is slow. The program also runs on the FX-602P where it is noticeably quicker. I have produced a shorter version specially for the FX-602P by changing the output part of the program.

Go to the code and documentation for the FX-502P version of the fractions program.

Go to the code and documentation for the FX-602P version of the fractions program.

Program for Factorials up to 253!

I discovered that the FX-502P can support numbers up to 9.9999999994910499. This program is the proof. I believe that you can't do this on the FX-602P, because numbers of 10100 can't be generated. Only look at the documentation if you're not going to try the challenges without hints because this is the solution to one of them and a big hint to others.

Go to the program and documentation for the factorials program.

Program for Testing Your Multiplication Tables

This trivial program tests your memory of the multiplication tables that you should have learned (or should be learning) at school. It tests the tables from the 3 times tables to the 12 times tables. (These limits would be easily modifed if you want to stop at the more logical 10 times tables). I had great fun using this program with friends at school. There's a FX-601P/FX602P version with more elegant output.

I wasn't able to convert this program to the FX-7000G because of the lack of a PAUSE but I did write a version for my HP48S. The HP48S has random number generator that appears random, which is more than I can say for the FX-502P. (It may be my imagination but the FX602P appears better.) The HP48S RPL program is much more complicated because it used alarms programmed to go off a short time in the future to mark the result. The HP48 program is available below.

Go to the code and documentation for the FX-501P/FX-502P version of the tables tester program.

Go to the code and documentation for the FX-601P/FX-602P version of the tables tester program.

Go to the code for the HP48 tables tester program.


I've learnt quite a bit about the FX-502P that is not in the manual. (Is this a sign of a wasted youth?) For your amusement I have set the challenges below.

Calculate and Display factorials up to 253!

Any geek will tell you the maximum input value to a factorial function of any calculator whose maximum number is 9.9999..E99 is 69. However although the specification of the FX-502P agrees with the above, it is possible to write a program to calculate and display factorial 253. Try it. (This gives the last result below 1E500). I don't believe it is possible to write such a program on the FX-602P. My solution has been tested and shown not to work on the FX-602P, so probably won't work on the FX-601P either.

Go toHints for the writing the factorial program

Go to my solution for the factorials program.

Generate the Character Set

Try to isolate the non-numeric character set and store each character in a memory. The character set of the FX-502P is 0 to 9 (obviously) and then in ascending order o, P, C, E, - and ' ' (i.e. the space character). The F character is excluded because it appears to have the same value as the o character. 'F' exists Mode 2 and not Mode 1. The reverse is true for o. Should you manage to isolate C & E you'll discover a problem. The presence of either on the screen, on their own, results in the locking of the calculator. A way round this is to generate them in negative form.

Go to hints for the generating the character set.

I don't believe that a solution is possible on the FX-602P unless you upload a memory dump that was created on the earlier FX-502P (or probably FX-501P). My solution is available.

Storing Numbers that aren't cleared by INV MAC or switching off

Store numbers somewhere that are not cleared after clearing memories or clearing programs (INV MAC in both modes 1 & 3) or switching off the calculator. My solution to this requires the solution to the Character set problem above. (I used to store my financial details in some of these 'secret' memories).

Go to hints for the storing numbers than aren't deleted.

Go to the solution.

Other Software Quirks

This is a collection of quirks sent to this site to get the non-numeric characters and access the L-registers

Go to Casio FX-502P quirks.


Photographs of the Internals

After the index of the FX-502P's manual there are a list of precautions, the first of which includes the statement 'Never disassemble it'. So of course soon after I got it, as a teenager, I dismantled it. It comes to pieces easily as do the fx-120, fx-550 and the fx-7000G (unlike my rather impregnable HP19BII and HP48S and difficult HP31E).

Go to pictures of some of these in disassembled form.


Let me state here and now that the Casio FX-502P is generally a robust device, as are other Casio products in my experience... however there have been problems.

Paint Work

The first problem I had with the FX-502P was a problem experienced by many people who had the FA-1 cassette interface, judging by the other pictures of the FX-502P on the web. The problem is that the brown paint around the screen and top 2 rows of buttons is rubbed away at the edges of calculator. This caused by the friction of taking the calculator out of the wallet.Picture of the damage.(86kB)

Power Switch

The power switch of the FX-502P is of a mechanical type and after many many operations mine started to fail. The mode of failure is to prevent the operation of the following buttons: AC, INV, P0 and GOTO. (I suspect that this is related to disabling the On function of the AC button when the calculator's power switch is in the OFF position.) The problem is metal fatigue. Replacement power switches weren't available when I requested one, but the 2 bits of springy metal, that act as contacts were. These pieces of metal appear to be common to other Casio calculators of this era, but the assemblies with the plastic switches are not. It was necessary to weld the metal contacts into the plastic switch. This I did with a soldering iron. Sadly when I last requested the part from the Casio Services Department (about 1993), I was told that these contacts are no longer available. My current partial effective solution is to short out the contacts on the board with a piece of aluminium foil that has been Sellotaped down. If you've found a source of the original contacts or have a better solution I'd like to hear from you.(How to contact me.)

The reason for the cracked screen of my machine is partly down to the faulty switch. I had discovered that applying a bit of pressure on the right hand side of the case would sometimes bring the calculator back on. Unfortunately the calculator had just lost the answer to a long awaited Simpson's integration that I was going to use to check some symbolic integration that I was doing at university. It wasn't going well and my 'bit of pressure' was more of a thump and that broke the screen. The screen is glued in and would not be easily replaceable even if it were available.


The plastic case, or wallet, that holds the calculator broke along the hinge. I'm on my 2nd .. or is it my 3rd? They've all had written on them 'Casio Programming Calculator' like the calculator itself. This is rather strange because the calculator is not very useful for programming because it doesn't support HEX. The FX-602P has the the more accurate inscription 'Casio Programmable Calculator'.

External Links

Here are some links to other calculator related sites

This site is Peter Martin 2003-2016.