LF15C - Firmware for the DM15

A 3rd Party Firmware for the DM15 family of calculators

• Full development history in HP Forum thread New firmware for the Swissmicros DM15L

• LF15C is written by HP Museum Forum member jebedeo
• It is a replacement firmware for the Swiss Micros DM15C & DM15L calculators.
  • also runs on the original DM15 credit card version no longer in production
• It is not an emulation or an exact simulation of the HP15C
• It runs directly on the hardware without an emulation layer.
• It is very much faster than the stock firmware
• It has full-time complex number support
  • including display of the full real & imaginary parts on the LCD together 3.345 +22.356 i
• It has a 4-level stack with full-time 2-level display of X and Y
• All the main HP15C functions are included with the exception of Matrix support

• sudo lpc21isp LF15C_250408.hex /dev/ttyUSB0 115200 1200
• Press hidden reset button
  • firmware is flashed
• press hidden reset button to start new firmware

The new Swiss Micros firmware V33 changes the behaviour of the bootloader, and it appears to be impossible to flash 3rd party firmware when the calculator is running V33 or later.

The firmware appears to flash correctly, but on reset it will not start

The solution is to downgrade to V32 first, and then install LF15C

• sudo lpc21isp DM15_M1B_32.hex /dev/ttyUSB0 115200 1200
• press hidden reset button
  • firmware is flashed
• press hidden reset button to start V32 firmware
• sudo lpc21isp LF15C_250408.hex /dev/ttyUSB0 115200 1200
• press hidden reset button
  • firmware is flashed
• press hidden reset button to start new LF15C firmware

• The Swiss Micros Voyager Update Tool will work to install LF15C
  • Do not use the new Web Update tool
• The same caveats regarding installation after using the Swiss Micros V33 apply
  • First downgrade to V32
  • Then flash with LF15C
• You need to use the hidden reset button in all cases.

• The Firmware files are available from the HP Forum Thread for this firmware - at the foot of Post #1
  • the version attached to Post #1 is always the latest available.
• At present (Jan '26) there is also a beta version which is being used to test various compiler optimizations, and is buggy and best avoided.

• Swiss Micros
  • V32 Firmware DM15_M1B_32.hex
  • Voyager Update Tool Voyager Firmware Update Tool

• Full time complex stack shows real & imaginary parts together as e.g. Rectangular: 3.45 +4.34 i or Polar: 5.5442 ∠51.5177
• maximum number range approx. ±1.797 x 10³⁰⁸
  • largest integer factorial 170fx! = 7.2574 E306
• smallest positive number approx. 1.00 10^-323 before 0 is returned
• Precision 15 decimal places

• π displays as 3.14159265358979
• e displays as 2.71828182845905

• Fingerprinting - see Fingerprinting

9SINCOSTANATANACOSASIN9-

-1.6584 x10 ^-10

• User Programs can be saved/loaded via USB Serial port using a terminal emulator such as Putty

• LF15C uses binary floating point representation, rather than the more common BCD.
  • This improves the speed but introduces occasional small rounding errors

Example (Click to view)

• Fix / Sci / Eng display formats
• √x / x²
• e^x / Ln
• 10^x / Log
• y^x / %
• 1/x / Δ%
• Sin / ASin
• Cos / ACos
• Tan / ATan
• Hyperbolics of Sin/Cos/Tan
• CHS / ABS
• EEX / π
• Deg / Rad / Grad Angle Mode
• →H.ms / →H Conversions
• →Rad / →Deg Conversions
• X!
  • integer, non-integer, negative and complex support
• Statistics
  • Σ+ two variable accumulation
  • mean
  • standard deviation
  • Linear Regression
    • slope / intercept
    • ŷ estimation / r correlation coefficient
• Combinations / Permutations
• Usual 4 level stack manipulations
  • Last x
  • Roll Down ↓
  • Roll Up ↑
  • Swap x ↔ y
  • Swap x ↔ any Storage Register
• 100 storage registers (numbered 00-99)
  • capable of saving Complex Numbers
• Indirect Register pair I / (i)
• Indirect Program Label / Line number addressing via Register I
• Random Number Generator
• Rounding
• Fractional / Integer
• Usual Keystroke Programming features
  • SST/BST
  • LBL
    • LBL A - E
    • LBL 00 - 99
  • DSE / ISG
    • including usual loop control indexing
  • Logical tests
  • Branching
    • GTO
    • GSB
    • RTN
  • PSE
  • R/S
• SF / CF / FS?
  • 10 user flags for program control
• Solver
  • can be used via a program
• Numerical Integration
  • variable precision via display digit format
  • can be used via a program
• quick clear of
  • Statistical data
  • Individual Program
  • All stored Programs
  • Storage Registers (0-99, I and (i))
• Full digit mantissa preview

• Matrix functions
• User Mode
• Memory management
  • partitioning between Storage Registers and Program Space is not required or supported

• Real Time clock
• Switchable 1-line display option (V33 feature)
• CPU speed switching
• Display Font options
• Adjustable LCD contrast
• Various self-tests
• Conversions & Constants (V33 feature)

• Very much faster than stock DM15L firmware … see Benchmarking

• The stack is permanently in complex mode and operates slightly differently to the stock HP15C

Press f I in normal mode to create & destroy a complex number from ⇔ to y and x on the stack.

Example (click to view)

Make a pure imaginary number by using fRe<>Im

Example (Click to view)

• f →R and g→P do NOT to convert x and y stack levels between Rect and Polar values as in the HP15C
• →R and →P are Mode Switching commands for the whole complex stack.
• When in Polar mode ALL Complex numbers on the stack are in Magnitude / Angle format.
  • The angle format can be Deg or Rad as appropriate

Example (click to view)

• Mode can be switched at any time - perhaps switching to Rectangular to enter a Rectangular format number, when working in Polar, and then switching back to Polar once it's been entered on the stack..
• Intermediate calculations can be done whatever mode is current.
  • this is unlike the HP15C, where complex arithmetic has to be done in Rectangular format - and Polar format numbers must be converted → R first.
• To confirm the mode in use an annunciator P is always present when in Polar.
  • No P means Rectangular mode is active.

Example (click to view)

Similar features to the standard HP15C, with differences due to increased Program Label numbers

Indirect Register pair I and (i) work in the usual way

Example (click to view)

As in the HP15C you can also indirectly address Program Labels using the contents of the I register to point to the label required.

The HP15C allowed 20 numerical Program Labels 0 - .9 which meant indirect addressing for Labels A - E was done by reference to 20 - 24 in Register I

LF15C has 100 numerical Program Labels so….

Store 00 - 99 in I to address numerical Program Labels 00 - 99

Store 100 - 104 I to address Program Labels A - E

Using GTO I or GSB I in a program will lead to a jump to the Program Label referred to by contents of Register I.

Changing Register I's contents (e.g. within a program) can then cause the execution of program to branch in different ways - this can be a very powerful mechanism!

Example (click to view)

LBL A
X^2
PI
*
RTN

LBL B
GTO I
RTN

Similar to the above, if the Indirect Register I contains a NEGATIVE number then a call to GTO I or GSB I will cause a branch to the absoloute Line Number referred to in I.

Example (Click to view)

0 Empty
1 LBL A
2 GTO I
5 RTN
6 LBL 88
8 X^2
9 PI
10 *
11 RTN
12 Empty

• 100 Storage Registers 00 - 99 are capable of storing Complex Numbers

• Factorial / Gamma x! works on integer (positive), non-integer (positive and negative) and complex numbers

• Program Mode shows human-readable text rather than HP15C op-codes
  • 2-line display of Program being edited

• Selection of logical tests can be done in usual HP15C fashion with TEST 0 - TEST 9
  • Test can also be selected from a scrolling list of options after initially pressing gTEST with the choice being made via soft-keys & LCD Prompts

• To run a program with a numeric label (i.e. other than LBL A → LBL E) press f LBL ##
  • e.g. f LBL 88
  • this is different than on the original HP15C where to run a label you used GSB##

• In program mode, f CLEAR PREFIX places the runTime opCode in the program. runTime writes to x the program execution time once it's executed.

• Deleting User Programs
  • Delete a single program : f CLEAR PRGM followed by a label
  • Delete ALL programs : f and long press CLEAR PRGM

• FIX/SCI/ENG don't round numbers unless gRND is pressed.

• fENGnn sets the number of significant digits as requested, UNLIKE the original HP15C where fENGn sets the significant digits to n + 1

• There are 10 user flags, from 0 to 9.
  • There are no LCD annunciators to show state, but flags can be set, cleared and tested for decision making in program branching

• Long press GTO in program mode to access go to label feature (single press in run mode)
• Long press GSB in program mode to access go to line number feature (single press in run mode)

• When running a program step by step, a long press on SST doesn’t execute the current step.

• Unused Keys
  • f USER, gMEM, fDIM, fMATRIX and fRESULT are not implemented and don't do anything at the moment.

• Serial Port dump info : https://www.hpmuseum.org/forum/thread-20046-post-194697.html#pid194697
• Serial Port settings
  • Rate : 57600
  • Data : 8 bit
  • Stop : 1 bit
  • Parity : None
  • Flow Control : None

ALWAYS INCLUDE AT LEAST ONE TRAILING ZERO FROM THE STRING OF DIGITS REPRESENTING THE MEMORY DUMP

• To extract a dump from calculator press and hold STO
  • the string of digits can be copy/pasted into a text file for storage
  • it is only necessary to keep one final zero - the rest of the zeros can be ignored
• To upload a previously saved dump
  • copy it to clipboard and then
  • press and hold RCL until the terminal shows Paste PrgMemory:
  • in Putty ShiftInsert to paste clipboard text into terminal

Tabulated List of LF15C firmware versions

• LF15C program dumps Program dumps for LF15C