HP41CL physical ports -or- how many physical ports do you require with the HP41CL?


More 41CL stuff!

When looking at the physical use of ports on the CL many users have questioned whether installing the time module internally and/or moving the RS232 jack to another location (side) would make more sense.

My short answer would be yes IF the free physical ports are required. Remember, all the existing ROMs are available on the CL board and can be invoked by the CL plug commands. There are a few exceptions such as the timer module and others listed in the manual:

HP 41CL home page

With this in mind do you NEED to internalize the time module or move the rs232 jack?

Again from the manual, the time module is physically installed in any PORT, although PORT two is the most convenient for me. It leaves PORT three for the IR or HPIL modules. Physical PORT four is for the card reader (PORT 4 LOWER must remain free as the card reader functions install in PORT 4 LOWER).

The following is the basic physical configuration:

table 1: Free ports with time module and RS232 jack in place:

PORT 1 LOWER YNFS (CL functions required, see manual)

figure 1: Basic configuration.

As you can see from table 1 the RS232 jack and the time module take no PORTs away from ROM image use. PORT 1 LOWER is taken over by the CL board for functions as does any physical module which takes over specific addresses. This still leaves PORT 1 UPPER free for STAT or any other ROM image occupying less then half a page.

The timer module behaves the same. Although the physical port is taken up, it does not occupy PORT 2 therefore leaving it free for a ROM image such as the full page ADVANTAGE module.

So you are left with two physical ports for physical module use. In figure 2 the IR module has been removed for the HPIL module. If using the HPIL to drive an HPIL printer then the IR module should be removed. If you are using the IR module with the HPIL then the HPIL module should have the printer switch set to disabled. (edited to reflect Montes' reminder that the HPIL module HAS a printer enable, disable switch.)

Figure 2. IR removed and HPIL installed with Disc drive:

In figure 3 the HP 41CL now has the HPIL and the Card Reader installed and linked to the HPIL cassette:

So now two free physical ports contain the HPIL and the card reader.

The calculator is currently configured with the following physical modules and ROM images:

Table 2: VIRTUAL STATUS (non phyical ROM images):


Table 3: PHYSICAL STATUS (physically inserted modules)

PORT 1  RS232 JACK  technically not a ROM at all as it just
occupies the space.
PORT 3 IR MODULE swappable with HPIL or others
PORT 4 CARD READER requires PORT 4 LOWER be free of virtual ROM

I cannot foresee any need to free up physically the two upper PORTs; 1 and 2. Esthetically I like the RS232 jack in place as it keeps the calculator case free of modification. But that is my opinion.

Of course there may be a reason or use by some one else that requires more then 2 open ports be available. So unless someone comes up with a valid reason to open up the two upper ports I say leave well enough alone ;-)

Just some ramblings (due in part between the CL users to internalize the timer module and move the RS232 Jack).

Cheers, Geoff

long live the CL (boy is it fast in turbo50!!!!)

Figure 4: overlay and modules, early photo, move the IR to PORT 3 in your mind please!

Edited: 22 June 2011, 6:05 p.m. after one or more responses were posted


Hi Geoff:

Why are you still using the card reader? The only reason I can think of is the card reader is very portable compared to the 9114B and if your 41C loses it mind via static discharge, you can more easily reload your programs during a flight. Do you bring multiple 41Cs with you when you're in the air? I remember you mentioning that one time you had your 41C with you and it locked up pretty tight during a flight. If your 42 lost it's mind while up there, the only way to recover is a lot of keyboard typing.

I wonder if the 41CL is more or less sensitive to static electricity than a 41C?


Edited: 21 June 2011, 9:12 p.m.


Hi Gerry

The 41C locked up tight when the Clonix module started to melt. The thinking at the time was that the Clonix had suffered a latch out and allowed 6 volts to course through it!

At the moment, I have the 41CL, 42S for backup and the 71B as something to play with all in my bag along with the IR printer and card reader.

The CL has performed admirably (only one flight thus far without static repercussions.) One flight is not statistical enough though ;-)

The card reader is for back up away from home (you were correct, portable) as it fits in the flight bag with the cards. I did use it this flight but that was in London at the hotel as I crashed it with some non creative conflicts while experimenting with the roms. At home the cassette or the disc drive are the prefered methods of reloading!

The 41's really hate the HPIL and IR modules in ports simutaneously and on the 41CX this creates an alarm sequence that only MEMORY LOST will correct. On the CL it creates a nasty ALPHA display when you try to XEQ an alpha command. The only way out is to reboot.

So yes the card reader is still the best back up. At least until I create a rom image with clonix or the pil box. Both I have to dig out and start playing with. Once my HP is backed up to a ROM image then EVERYTHING I need is in the CL board!

Another reason to use the CL now that it is as fast as the 42S is because during a calculator crash it can be recovered WITHOUT all that typing...


Just dug up my University cards for the 41. 15 cards with a quite a few dedicated routines for data analysis and collecting. They all work perfectly, even after 26 years!

Edited: 21 June 2011, 9:43 p.m.


What no 34s?????

- Pauli


Pauli ;-)

just waiting for the overlay from Eric to make it easier. I have a clear cased prototype.

Also working on the chapter about the HP 41C because it has to include a section on the CL now.

Cheers, Geoff


Hopefully it will make a nice addition. Programs stored in flash are unlikely to get lost or accidentally erased.

- Pauli


That is great and solves the problem of having to retype. You will notice that the three calcs I carry all print and two have easy backups.

I need the print capability for the cockpit! I need the 34S to have fun with and will program when the Postal service up here resumes work. (currently on strike so no USPS stuff makes it here!).


If we only had some more capable hardware...

What's missing:

Memory for code and data,
Better display,
Better I/O (e.g. an IR eye and/or USB port).

I still have the feeling that we've done a pretty good job, given what the 20b/30b provide as a hardware basis. But we can't beat the 41CL or 42s in many respects.


Marcus any thoughts on a serial port for the 34s??? :-)

The one last thing I'd like to add is some serial IO but it will require hardware modifications like the time and date stuff.

- Pauli


Marcus any thoughts on a serial port for the 34s??? :-)

The one last thing I'd like to add is some serial IO but it will require hardware modifications like the time and date stuff.

I'm thinking of it. The idea is to add a 2.5 mm jack like the TIs or Casios have. There are USB cables available for Casio calculators which are made of an FTDI chip. The problem: They work on 5 V. A better idea would be to use the 3V variant of the FTDI USB to serial cable and tell people how to add the proper plug to it. Here is the data sheet: DS_TTL-232R_CABLES.pdf.

Are the special plugs used by HP for the programming interface publicly available? I don't like how the plug and cable protrudes from the back of the device so that you cannot put it flat on your desk while connected but this would prevent modifying the case.

Edited: 22 June 2011, 5:21 a.m.


The IR Printer module should only be in the calculator at the same time as the HP-IL module if the HP-IL module Print Function switch is set to Disable. Otherwise both modules will be trying to drive the ISA bus whenever the operating system is trying to find a function. This isn't good for either module. What you are probably seeing is the result of bad levels on the ISA bus during this time. Who knows how the logic in the CPU (either in a 41C or a 41CL) are going to respond to this.


Somewhere in the last 35 years I knew this! After 35 years using this calc and HPIL I still feel like a novice! Of course it would make sense that there is a conflict, they both support printers. How basic is that logic!

So still learning or being reminded! Of course I could have re-read my HPIL module manual and seen this:


top post now edited to reflect Montes' reminder ;-)

Edited: 22 June 2011, 3:41 a.m.


Geoff, you're right about that. I knew that too and it didn't connect until Monte mentioned what is obvious and logical. It makes me feel old.

I wanted to mention that the link to 41CL manual in your first post doesn't work for me. I'm also starting to put together some questions I have about the 41CL just to understand how it works. For instance, is it possible to place the 41CL into a state whereby to recover, the static RAM would have to be cleared; in essence doing a 'first-birthday' on it? Is it possible to dump the entire contents of a fully configured 41CL to a PC via the serial port or using HP-IL to a tape drive of floppy (like a WALL command), to make recovery easier if the answer to my first question is yes. I am fascinated by the 41CL and how it will fit with my other 41 equipment. Geoff, your postings are very helpful in figuring that out so thank you. I just wish I was out there on the bleeding edge with you. I have a knack for instinctively finding bugs and 'issues' with new gear. Just ask my boss!


Edited: 22 June 2011, 1:11 p.m.


There is a typo in the link above. Here is the real one: http://www.systemyde.com/pdf/sy41cl.pdf

The information page is: http://www.systemyde.com/hp41



Please send me an e-mail, I am interested in getting some information regarding cost for the 41CL.



Link repaired in posting #1


I've been reading the 41CL manual to figure out which of my 41s I can use to upgrade. I have a 41CV with rounded display corners, which makes it a half-nut. It's serial number starts with 2641S which, as I remember, means it was built in 1986 in Singapore. In the 41CL manual, it says:

"If the light part of the display has square corners, like those shown below, the calculator is a candidate for replacing the CPU circuit board".


"If your 41CV/CX has a serial number starting with “2003” or larger it uses the correct display driver".

So, it appears that this 41CV is NOT a candidate for the 41CL board. Am I correct?



Correct. Half-nuts cannot be upgraded.


Here for those that are interested are shots elaborating the difference between the fullnut (older) and the halfnut versions of the HP 41C, CV, CX

-There are fullnut 41C's, 41CV's and 41CX's
-There are halfnut 41CV's and 41CX's (if you have a 41C halfnut
then you have a fullnut that was repaired under warranty and
a very rare nut indeed, infact it should be called a rarenut)


Fullnut with squared LCD corners:

Halfnut with rounded LCD corners:


Open the case and you see on the left a full nut removable board and on the right a half nut soldered board.

As above but with the film removed:

You can see the removable fullnut logic pca on the left and the smaller soldered pca on the right. Of course it cannot be a swap as the physical boards are completely different. Montes' HP41CL will function in place on the left board style only. Also note that the half nut has the IC imbedded on the keyboard pca precluding any swap and has a completely redesigned keyboard and logic pca.

Hope the visual helps

Edited: 23 June 2011, 5:17 a.m.

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