dbl xmem module...


Hi there, I recently bought a used HP41CV with an X Functions module and a "dbl xmem" module. What is this exactly? Is there a manual anywhere for it? Thanks in advance, Andreas


The HP 41 instruction set may be enhanced with the X Functions module, which adds functions that allow for alpha string manipulation; conversion between numeric values and alpha characters (and viceversa); programmable keyboard assignments; programmable size command; flags management; block register moves; and others.

The X functions module also introduced the concept of extended memory: registers that are not addressable by STO or RCL, or usable for running programs. Such extended memory works more or less as a solid-state floppy disk, in which you could save and later recall programs or data files. There were special functions to check the extended memory directory, to create or delete files, to access data records and to load or save programs. Although logically separated from main memory, extended memory will not survive a MEMORY LOST situation (I think it should survive, or at least ask the user what to do).

The X Functions module contains the ROM to support such functions, and also 127 registers for extended memory. There also are extended memory modules, which have no ROM but hold 238 extra registers, so the maximum extended memory was 603 registers (one X Functions and two X Memory modules). When using two "regular" extended memory modules, they could not be installed on ports combinations (1 and 3) or (2 and 4). The extended memory modules are useless without the X Functions module.

From your description, it seems that you have a non-standard double extended memory module, which may hold 476 registers.

The HP 41CX included the extended funtions on the basic machine, so the X Functions module is not needed for the 41CX. As you have a 41CV, both the X Functions module and the "double"(?) X Memory module will be useful for you. You can browse the names of the functions using a CATALOG 2 command, but you will need the Extended Functions/Memory manual to understand them. (I think it is available on this Museum CD set).

Many of the string and file manipulation functions are useful when you connect your HP41 to HP-IL devices.

Some extended functions were also incorporated to the HP42S instruction set, but not the extended memory architecture.

Hope it helps.



AFAIK HP did not produce any "double" modules.

Several people have constructed double memory modules, and I guess the same is true of X-Mem modules.

I think you'll find that it's a custom job, possibly done by an enthusiast. Check the obvious things:

1) does it look like it's been taken apart

2) is it unusual in some other respect (like the little handle doesn't come out)


It is certainly custom module doubling. In its heyday there were many people doing module doubling, and a few doing module tripling. EduCALC catalog offered the service of SOS to do the doubling for you. In 1983 I did two myself. I doubled a TIME MODULE and a MATH PAC. Also an EXRENDED FUCTIONS with EXTENDED MEMORY. These doubling freed up one of the precious four ports.

Extended memory combinations, and HP-IL related modules were the two most popular.

One thing to be aware of is it could not usually be done with two application pacs ... at least one of the modules had to be port addressed to a "system address". Recall that the HP-41 has an address structure supporting 64 KBytes. That breaks out to 16 pages og 4 kB. The three operating system ROMS (internal) are at pages 0, 1 and 2. I believe the TIME MODULE if installed always locates itself to page 5, regardless of being a CX or a C/CV installed in ports 1 through 4. The ports 1 through 4 can address 2 pages of 4 kB. Port 1 (8,9), Port 2 (A,B), Port 3 (C,D) and Port 4 (E,F).

Module tripling actually required milling out some of the plastic case on the application pac to make room, and filing down some of the epoxy sealer on the ROM inside the case. These were well documented in the PPC Journal in a column titled "Butcher's Block".

If anyone needs the information in hard copy, you can send me a self addressed stamped envelope ($0.55) to CHRIS CATOTTI, PO BOX 621777, OVIEDO, FL 32762-1777. Or you cam have all the information and much, much more if you buy the CD ROMS from the HP-Museum.


Is there a manual anywhere for those or any literature anyway? Can you still make those? How many x functions, dbl xmem modules can I have installed?


You can have only one X Functions and two X Memory modules installed at the same time. If your "DBL XMEM" is actually two XMEM modules in a single case, then that (plus the XFUNC module) is the only extended memory you can install. (The purpose of combining two modules into one is not to increase the amount of X memory possible, but to leave one more port available for plugging in another module of a different type.)

There should not be any special manual needed for a DBL XMEM module, because as far as the calculator is concerned, it should work just like two ordinary XMEM modules. In fact, there is no manual needed for a regular XMEM module because all you need to do is to plug it in and use it. The commands for using X Memory are contained in the X Functions module. If you don't have a manual for that, you could get one by ordering Dave's CD set (look for "The Museum on CD" on the main menu of this site). It has complete documentation for your HP-41CV and any modules you're likely to find for it (including the XFUNC module).

In the meantime, here are a few commands you can use. EMDIR will show you the contents of extended memory. It also tells how many registers of exended memory each file uses, and how many registers are free. (Each register contains seven bytes.) If you have just plugged the modules in, or if you have cleared memory by turning the calculator on by pressing ON and BACKSPACE together (you'll get a "MEMORY LOST" message), then EMDIR will give a "DIR EMPTY" message in the display. Press BACKSPACE and you will see the number of registers free. With your XFUNC and DBL XMEM modules installed, you should see "600" in the display. That's the maximum number of X memory registers your calculator can handle.

You can copy a program from main memory to extended memory by putting the name of the program into the ALPHA register and executing SAVEP. To copy it back to main memory, put the name in ALPHA and execute GETP. Their are other commands to create data or text files and access them, but that's a little complicated to cover in a message here. (This one is getting too long already!) I highly recommend you get the Museum CD set and you'll have all the info you need on your calculator (and nearly every other calculator HP has ever made).

One more thing, in case no one has told you yet: Always turn the calculator OFF before inserting or removing any module. Though forgetting this usually doesn't cause a problem, it's possible to make the calculator lock up, or even cause physical damage to it and/or the module.

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