Systemyde 41CL User manual

41CL User Manual
© 2019, Systemyde International Corporation 1
41CL Calculator

41CL User Manual
© 2019, Systemyde International Corporation 2
Every effort has been made to ensure the accuracy of the information contained herein. If you find errors or
inconsistencies please bring them to our attention.
Copyright © 2013-2019, Systemyde International Corporation. All rights reserved.
Notice:
“HP-41C”, “HP-41CV”, “HP-41CX” and “HP” are registered trademarks of Hewlett-Packard, Inc. All uses
of these terms in this document are to be construed as adjectives, whether or not the noun “calculator”,
“CPU” or “device” are actually present.
Acknowledgements:
This project never could have succeeded without Warren Furlow’s excellent Web site hp41.org. And even
more important was his SDK41R6 software suite, for code development, and his V41 program for code
debugging. Numerous people have answered my dumb questions on the Web site hpmuseum.org, and the
book “Inside the HP-41” by Jean-Daniel Dodin was invaluable for getting a foothold on understanding the
HP-41 operating system and register usage.
Gene Wright was kind enough to be my voice at the HHC 2010 conference.
‘Angel Martincontributed valuable 41CL-specific software to the project.
Eric Rechlin made the labels for the front of the calculator.
Nate Martin modified his Port cover 3-D model specially for use with the serial port jack.
Benoit Maag provided the photograph of the different connector types.
Geoff Quickfall provided the photographs of the older display driver and corresponding capacitor fix.

41CL User Manual
© 2019, Systemyde International Corporation 3
Table of Contents
1. Introduction ......................................................................................................... 5
Can my calculator be upgraded? ................................................................7
2. Getting Started .................................................................................................... 9
Installing the 41CL Circuit Board ..............................................................9
Initial Software Configuration ....................................................................18
3. 41CL Extra Functions .........................................................................................20
Extra Functions Parameter Passing ........................................................... 21
MMU Functions ........................................................................................... 22
MMUCLR ...............................................................................................22
MMUDIS ................................................................................................ 22
MMUEN ................................................................................................. 22
MMU? .................................................................................................... 23
Turbo Functions ...........................................................................................23
TURBOX ............................................................................................... 23
TURBO2,TURBO5,TURBO10,TURBO20,TURBO50 ................24
TURBO? ................................................................................................24
Plug into Port/Unplug from Port Functions .............................................. 24
PLUG1,PLUG2,PLUG3,PLUG4 .....................................................25
PLUG1L,PLUG2L,PLUG3L,PLUG4L,PLUGP ............................26
PLUG1U,PLUG2U,PLUG3U,PLUG4U,PLUGH ..........................27
UPLUG1,UPLUG2,UPLUG3,UPLUG4 ..........................................28
UPLUG1L,UPLUG2L,UPLUG3L,UPLUG4L,UPLUGP ............. 28
UPLUG1U,UPLUG2U,UPLUG3U,UPLUG4U,UPLUGH ........... 29
Memory Block Functions ............................................................................ 29
YMCLR .................................................................................................. 29
YMCPY .................................................................................................. 30
Memory/IO Read and Write Functions ..................................................... 31
YPOKE .................................................................................................. 31
YPEEK ...................................................................................................32
Memory Buffer Functions ........................................................................... 32
YBPNT ...................................................................................................33
YBPNT? ................................................................................................ 33
YBUILD ................................................................................................. 34
Flash Memory Functions .............................................................................34
YFERASE ............................................................................................. 35
YFWR .....................................................................................................35
Serial Port Functions ................................................................................... 36
SERINI ................................................................................................... 37
BAUD12,BAUD24,BAUD48,BAUD96 ...........................................38

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© 2019, Systemyde International Corporation 4
YGETLB,YGETUB ..............................................................................38
YPUTLB,YPUTUB .............................................................................. 39
YEXP ......................................................................................................39
YIMP .......................................................................................................40
Miscellaneous Functions ..............................................................................41
YFNS? ................................................................................................... 41
Image Database Functions .......................................................................... 41
IMDB? ....................................................................................................41
Special MMU Functions .............................................................................. 43
MAPDIS ................................................................................................. 43
MAPEN .................................................................................................. 44
4. Error Messgaes ....................................................................................................45
5. Functions Summary ............................................................................................ 46
6. Image Identifiers ................................................................................................. 49
7. Memory Management .........................................................................................61
The MMU and program addresses .............................................................61
The MMU and data addresses .................................................................... 64
8. Programming the MMU ..................................................................................... 67
Library-4 .......................................................................................................67
The FORTH ROM .......................................................................................67
The HP Service ROM .................................................................................. 68
9. Image Database ....................................................................................................69
10. Patching Code ......................................................................................................78
11. Using HEPAX ...................................................................................................... 80
Patching HEPAX ..........................................................................................83
Enabling HEPAX Disassembly ...................................................................83
12. Serial Connector ..................................................................................................85
13. Time Clone Connections .....................................................................................87
14. Updating 41CL hardware ...................................................................................90
CPLD Programming ....................................................................................91
FPGA Programming .................................................................................... 92
Flash Programming ..................................................................................... 92
15. Revision History .................................................................................................. 93

41CL User Manual
© 2019, Systemyde International Corporation 5
Introduction
The 41CL design takes advantage of modern technology to significantly add to the
capabilities of the 41C system. In particular, the 41CL provides the following features:
• All features of an HP-41CX except for the Time Module. CX Time functions (the
software) are included, but a Time module plugged into a Port (or our Time Clone
mounted on the 41CL board) is required for full timer functionality.
• Full 600-register Extended Memory is built in.
• Support for the new 1024-register Expanded Memory.
• Over 390 plug-in module images are built in. Functions are included to allow these
images to be virtually plugged into a calculator Port and unplugged from a calculator
Port.
• Turbo mode, which allows the calculator to run at up to 50X normal speed. Actual
values available are 2X, 5X, 10X, 20X and 50X.
• Numerous empty pages (4K in length) of Flash memory are available for non-volatile
storage.
• 122 pages (4K in length) of RAM are available. All RAM is continuously powered.
• A sophisticated Memory Management Unit (MMU) allows full access to the large
physical memory.
• Support for fifteen Alternate Configurations, where each configuration is a compete
set of images to be plugged into the Ports.
• Full bus compatibility for the Ports, allowing the use of any peripheral designed for
the HP-41 system.
• A full-duplex serial port is available when the optional serial connector is used. This
optional connector uses a 2.5mm stereo jack mounted in a blank port cover.

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© 2019, Systemyde International Corporation 6
With these features, however, come some drawbacks:
• Power consumption is higher, at least while the calculator is off or in light sleep
(between keystrokes). Where the original HP-41 required about 10 μA while off, the
41CL requires about 110 μA. This will lead to reduced battery life.
• The original HP-41 could retain memory contents for several minutes while the
batteries were changed. Because of the higher current consumption, the 41CL only
retains the memory contents for a few seconds while the batteries are out. For this
reason, you should probably have an extra battery holder ready to go when changing
batteries.
• The advanced technology used in the 41CL is a double-edged sword. The Flash
memory, as well as the programmable logic devices used to implement the NEWT
microprocessor, only guarantee data retention for 20 years.
The table below shows the typical current drain for the 41CL under various conditions.
The serial port is powered up whenever it is connected to something with a valid signal
level.
No Time Clone installed Time Clone installed
Calculator State Serial port
off Serial port on Serial port off Serial port on
Off 110 μA 3.6 mA 340 μA 3.8 mA
Light Sleep
(between key presses) 3.6 mA 7.1 mA 3.8 mA 7.3 mA
Running (1x) (Note 1) 7.1 mA 10.6 mA 7.3 mA 10.8 mA
Running (50x) (Note 2) 12.1 mA 15.6 mA 12.3 mA 15.8 mA
Flash Erase (Note 3) 46.0 mA 49.5 mA 46.2 mA 49.7 mA
Note 1: Measured during a CAT 2 operation.
Note 2: Measured during a normal (not CPONLY mode) FLCHK? operation. See the
41CL Update Functions for details.
Note 3: This peak current lasts for less than 500 mS.

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© 2019, Systemyde International Corporation 7
Can my calculator be upgraded?
The 41CL is an upgrade created by replacing the CPU circuit board in a 41C/CV/CX with
the 41CL circuit board. This replacement is only possible for calculators that actually
have a CPU circuit board. The easiest way to tell if this is the case is to look at the HP-41
display. 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.
Hewlett-Packard changed the display driver circuitry in the 41 series during production,
and this change affected one component value on the CPU circuit board. The 41CL
circuit board implements the component value used in later production units. Units with
the correct display driver can be identified as follows:
• If your 41C (not CV or CX) has a serial number starting with “1954” or larger it uses
the correct display driver.
• If your 41CV/CX has a serial number starting with “2003” or larger it uses the correct
display driver.
It is theoretically possible to use the 41CL circuit board with the older display driver, but

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© 2019, Systemyde International Corporation 8
this requires soldering an extra capacitor to the calculator main board. Refer to the next
section for the details.
In addition to the display driver change, Hewlett-Packard also experimented with
different methods of connecting the CPU board to the main board. Unfortunately it is not
possible to identify units that used these different connection methods via the serial
number. Identifying such a calculator is a step in the installation process covered in the
next section.

41CL User Manual
© 2019, Systemyde International Corporation 9
Getting Started
The 41CL circuit board is designed to be a drop-in replacement for the original CPU
circuit board, and the installation is not difficult. However, certain precautions must be
taken to prevent damage to both old and new circuitry.
All integrated circuits are susceptible to damage from electrostatic discharge (ESD). If
you have access to an electrostatically protected work area by all means use it. If not,
make sure that you ground yourself immediately before starting the installation process.
The best way to keep from generating a static charge is to not move around while
working, so make sure you have everything required before starting the process. Do not
touch exposed conductors, and handle both the original CPU circuit board and the
41CL circuit board by the edges. The 41CL circuit board has a 2mm space around the
edges devoid of circuitry or components to facilitate handling in this manner.
Tools required for the installation are a small Phillips-head screwdriver, an Xacto knife or
similar, a pair of tweezers, and a small flashlight.
Installing the 41CL circuit board
Follow the steps below to perform the installation:
1. Read through all of these instructions before starting the installation process, to make
sure that you understand each step. We are not responsible if you damage or ruin
your calculator or the 41CL circuit board while attempting this installation.
2. Verify that your calculator is one that has a CPU circuit board. Only calculators with
“square corners” on the LCD display panel (refer to the Introduction section for a
picture) have CPU circuit boards.
3. Remove the battery case, by first sliding the case towards the top of the calculator until
the bottom end of the battery case pops free. Install fresh batteries.
4. Carefully remove the four rubber feet, using a pointed knife to pry up one corner of a
foot and a pair of tweezers to lift the foot from the case. Be careful not to damage the
feet, as replacements are difficult to find. They are attached to the calculator body
using double-sided tape which can usually be reused.

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© 2019, Systemyde International Corporation 10
5. Remove the four screws located in the recesses under the rubber feet. Be very careful
not to lose them, as they are essentially impossible to find unless you want to buy
10,000 of them. The screws are all #2-28 trilobular thread-forming types. Those at the
bottom of the case are 1/4” (they may be 3/8” if the calculator has been serviced),
while those at the top of the case are 3/4”.
6. Lift off the bottom case and the U-shaped center case section. Note the orientation
(front-to-back) of the center case section, because it not symmetric. Don’t worry if
your old CPU board looks slightly different from that shown in the picture below.
These boards went through several revisions during the life of the 41C series.

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© 2019, Systemyde International Corporation 11
The photo below shows an early HP-41C with the type of display driver chips that
will require an extra component if used for the 41CL. If your calculator looks like the
previous photo, with grey epoxy blobs, proceed to step 7.
The early display driver required a different capacitor value to control the time delay
for the auto-off function. The photo below shows the required 10nF capacitor
soldered in place. The type of capacitor is not critical, but it must be able to tolerate 6
volts.

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© 2019, Systemyde International Corporation 12
7. STOP! Before lifting the old CPU circuit board use a flashlight to look into the space
between the CPU circuit board and the base circuit board. You will be able to see
which type of connector is being used. The photo below shows the three types of
connector used by HP.
The connector style on the left has conductors wrapping three sides of the connector
and will appear white when viewed from the side. This connector type is difficult to
reuse and not really recommended.
The connector style in the middle is rare. It has conductors embedded vertically in the
material and will appear white or pale pink from the side. This connector type is
impossible to reuse, which is probably why it is rare. Unless you have a replacement
connector you should fnd another calculator to use for the conversion.
The connector style on the right uses conductors rolled around a tubular material and
will be shiny when viewed from the side. Being reusable, this type of connector is
suitable for use with the 41CL circuit board.

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© 2019, Systemyde International Corporation 13
8. Before removing the old CPU circuit board, carefully inspect all four screw posts on
the front case. If they are cracked or broken (a common problem) they will need to be
repaired before re-assembling the calculator. Instructions for this repair can be found
on the Museum of HP Calculators web site. Repair the screw posts before proceeding
any further.
9. Using only the edges of the board, carefully lift the old CPU circuit board off of the
base circuit board. The connectors will usually remain in place on the main circuit
board. If by chance they do not, restore them to their proper location. The two halves
of the connector are usually held together by a flexible piece of plastic that fits over
the two screw posts just like the CPU circuit board. Some connectors were held in
place by the black spacer hooking down around the ends of the connectors by about
1cm. This will interfere with several components on the bottom of the 41CL board.
The spacer and connectors should look like those in the photograph below for a
proper installation. If the spacer looks different, trim the excess material so that it
looks like the case shown in the previous photo on the left or the right.
10. Using only the edges of the 41CL circuit board place this board on the main circuit
board, with the two lower screw posts going through the holes in the 41CL circuit
board just as they did with the original CPU circuit board. Use the antistatic bag
containing the 41CL circuit board to store the old CPU circuit board. Do not throw
away the old CPU circuit board, as it may still have utility in the future. If you don’t
want to store the old CPU circuit board, send it to us. Early versions of the 41C used
nuts screwed onto the posts to hold the CPU board in place. DO NOT use these
nuts without first installing a nylon washer bewteen the 41CL board and each
nut! The nuts are large enough to damage traces on the 41CL board! If you are
installing the optional serial connector, proceed with the steps below. Otherwise skip
ahead to step 15.

41CL User Manual
© 2019, Systemyde International Corporation 14
11. The 41CL circuit board contains a simple RS-232C serial port. The Receive Data,
Transmit Data and Ground signals for the serial port are present on the programming
connector for the CPLD on the board. The optional serial connector contains a plug
for this connector, connected through a cable to a 2.5mm stereo jack mounted in a
blank Port cover. The serial connector is designed to occupy Port 1 on the calculator
only. While it can be plugged into any other Port, doing so will interfere physically
with the remaining Ports because of the cable.
CAUTION! The tension holding a 2.5mm plug in the serial connector jack is higher
than the tension holding the blank port cover in the calculator body. This means that
trying to pull out the plug will tend to pull the blank port cover out of the calculator,
potentially damaging the internal connections to the serial connector jack. So always
remember to hold the blank port cover in place when attempting to remove the serial
port plug from the calculator.

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© 2019, Systemyde International Corporation 15
12. Insert the connector end of the serial connector through Port 1 and in between the
space between the calculator body and the flexible Port connectors
13. Route the cable down the side of the calculator body, between the edge of the battery
compartment and the outside of the case. It is helpful to use double-sided tape to hold
the cable in place next to the battery compartment between the Port and the battery
charger Port.

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© 2019, Systemyde International Corporation 16
Note how the cable turns sharply near the bottom of the Port to take advantage of the
space that will exist between the upper and lower halves of the case. It is easiest to
route the cable with the center section of the case in place on the lower case half.
14. Carefully plug the connector on the cable into the connector jack on the 41CL circuit
board with the “CP” label next to it. This is the programming connector for the
CPLD. The connector used is very fragile and was not really designed for multiple
insertions, so take your time, but make sure the plug is fully seated in the connector
on the 41CL circuit board.
The two connectors for programming the CPLD and the FPGA on the board are
identical, and plugging the serial port connector into the wrong one will damage the
board. The 41CL circuit board is shipped with a blank plug in the FPGA connector to
prevent accidently inserting the serial connector in the wrong jack.
This step is where the double-sided tape holding the cable in place is useful, as it
keeps the cable from popping out of the channel on the side of the calculator where it
resides.

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© 2019, Systemyde International Corporation 17
15. Carefully fit the center case section (with the proper orientation) and bottom case
back together with the remainder of the calculator body. If you installed the serial
connector be very careful not to pinch the serial cable between the case halves.
16. Re-install the four screws. The proper way to do this is to slowly turn the screw
backwards until you feel the screw threads “click” into the threads in the post.
Carefully tighten the screws. Do not over-tighten the screws as you risk cracking or
shearing off the screw posts. It is best to hold the case sections tightly together with
one hand while tightening the screws with the other hand, as this reduces the stress
the screws place on the screw posts and case pieces.
17. Re-install the battery case (with the new batteries) and turn the calculator on. If there
is no response the flexible connectors are not completely connecting the 41CL circuit
board to the main circuit board, and you will need to either tighten the screws a little
or reform the circular connector slightly. If garbage rather than the MEMORY
LOST message appears, try removing the battery pack for 30 seconds and re-
inserting it again. The display controller contains its own power-on-reset circuit,
which sometimes does not properly synchronize with the CPU, leading to garbage in
the display on power-up. This occasionally occurs even in the original design. If this
doesn’t work try XEQ ALPHA TURBOX ALPHA, which guarantees operation at
normal speed, even though the Turbo mode is supposed to be disabled at first power-
on.
18. Once the 41CL circuit board installation is verified working, reinstall the calculator
feet, and proceed to the initial configuration of the software.

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© 2019, Systemyde International Corporation 18
Initial Software Configuration
The 41CL includes a set of functions that provide access to the new features of the
NEWT microprocessor. When power is first applied or when the calculator is reset,
resulting in the MEMORY LOST message, the 41CL Extra Functions are mapped to
Page 7 to allow you to do the initial configuration of the calculator. This Page 7 mapping
is enforced by the hardware for as long as the Memory Management Unit (MMU) is
disabled.
During the initial configuration the 41CL Extra Functions must either be moved else-
where so that Page 7 can be used by HP-IL Peripherals or the Page 7 entries in the MMU
must be programmed to point to the 41CL Extra Functions after the MMU is enabled.
Until the 41CL Extra Functions are moved from Page 7 HP-IL will not be available, and
an HP-IL Module should not be inserted into the calculator because this will lead to bus
conflicts.
The 41CL Extra Functions (YFNZ mnemonic) uses XROM #15. If this is going to
conflict with another module that you want to plug in please refer to the “Patching Code”
section later in this document. Note that some third-party software (CL Utilities, for
example) requires the use of the XROM #15 version of the 41CL Extra Functions.
The 41CL Extra Functions image resides in an area of Flash memory that is protected
from modification, so that it should always be available.
As you become more familiar with the 41CL, you may prefer to use the 41CL Extreme
Functions (YFNX mnemonic), which provides a more convenient user interface that
prompts for user input.
The minimum sequence for the initial configuration uses three 41CL Extra Functions
(these functions are explained in the next section). If you don’t need to use the advanced
features of the 41CL this is sufficient for the initial configuration. This sequence is:
1. XEQ ALPHA MMUCLR ALPHA initializes all of the MMU entries in memory, mak-
ing it safe to enable the MMU in the third step.
2. ALPHA YFNZ ALPHA XEQ ALPHA PLUG1L ALPHA plugs the 41CL Extra
Functions into the lower half of Port 1 (which is Page 8). Since the MMU is still dis-
abled this has no effect yet. Note that any port can be used for the 41CL Extra Func-
tions. Plugging the 41CL Extra Functions into a Port allows the use of HP-IL.
Or you can use ALPHA YFNZ ALPHA XEQ ALPHA PLUGH ALPHA to plug the
41CL Extra Functions into Page 7. This saves half of a Port, but means that HP-IL
(including an HP-IL printer) will not be available. Since the MMU is still disabled
this has no effect yet.

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© 2019, Systemyde International Corporation 19
3. Finally, XEQ ALPHA MMUEN ALPHA enables the MMU, which starts the redirec-
tion of either Page 8 or Page 7 to the 41CL Extra Functions. When using Page 8 any
ROM module plugged into Port 1 will not be seen by the 41CL. However, Port 1 can
still be used for modules with a fixed address such as the 82143A Printer, the 82160A
HP-IL Module, the 82182A Time Module or the 82242A IR Printer Module.
Enjoy your new 41CL calculator! The only thing to remember is that the 41CL Extra
Functions (or the 41CL Extreme Functions)must remain plugged into a Port for the new
features to be available.
If you inadvertently plug another module image into the Port used by the 41CL Extra
Functions, taking the place of these functions as far as the OS is concerned, try to recover
by doing XEQ ALPHA YRES ALPHA. If this doesn’t work the only way to recover is
either via BACKSPACE-ON (causing a MEMORY LOST condition) or by
momentarily removing the battery pack.
The 41CL Extreme Functions allow the user to protect the MMU programming against
accidental modification, and automatically protects itself against accidental deletion.

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© 2019, Systemyde International Corporation 20
41CL Extra Functions
The 41CL Extra Functions are required to provide access to the new features of the
NEWT processor that powers the 41CL calculator. Depending on your level of
experience and how adventurous you are, you may not need all of these functions.
The majority of users will only need the MMU Functions, the Turbo Functions, and the
functions that allow you to Plug and Unplug module images to and from the calculator
Ports.
If you are a HEPAX user you will need the Memory Block Functions and the Memory/IO
Read and Write Functions. Refer to the Using HEPAX section for the details of how to
do the initial setup of HEPAX memory.
Users interested in MCODE programming or building a custom module image may find
the Memory Buffer Functions useful.
The Flash Memory Functions are included for those users wishing to program the Flash
memory on the 41CL circuit board beyond the initial programming. Flash memory is non-
volatile, so it provides a convenient way to store information permanently.
The Serial Port Functions allow users to control the serial port on the 41CL circuit board.
Using the serial port will require installation of the optional serial port connector.
Advanced users interested in modifying or replacing the Operating System will need to
use the Special MMU Functions. These functions control MMU operation for the pages
of memory that contain the Operating System.
The 41CL Extra Functions are sufficient to use most of the new features present in the
41CL, but once you are familiar with the machine, we recommend upgrading to the 41CL
Extreme Functions. The 41CL Extreme Functions unlock several more powerful features
of your 41CL.