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VX-3 emulator

The program emulates the HD61700 microprocessor and uses the ROM dump from the original calculator, therefore it should function almost exactly like the real one.
It works on PC-compatible machines with Microsoft Windows operating system.

Files to download

Program version 04, updated 2025/01/09

vx3_emus.zip - Delphi 5 sources

vx3_emul.zip - compiled executable
Usage: extract the files into an empty directory, then run the program vx3.exe

The screenshots

Usage hints

• Following files contain the memory images, and are loaded when the program is started:

    rom0.bin     - processor's internal 6kB ROM
    rom1.bin     - external 128kB ROM
    charset.bin  - LCD controller's internal character ROM of size 1.5kB
    ram0.bin     - 40kB RAM
    register.bin - processor's internal register file
  

• The updated files ram0.bin and register.bin are saved when the program is terminated. If they weren't found, they will be created. In such case the memory has to be initialised with the ALL RESET button.
• The emulator can be operated with the mouse or the keyboard. Special function keys:

    Cursor keys: corresponding arrow keys
    Page Up:     red S
    Page Down:   CAPS
    Esc:         BRK
    Insert:      INS
    Delete:      DEL
    Backspace:   BS
    Enter:       EXE
    F3:          suspends the code execution and opens the debugger window
    F4:          invokes the communication utility
    F9:          Reset

Peripheral devices

Serial port

The communication utility invoked with the F4 key is equivalent to a terminal program used with a real calculator. Button functions:

[Send]

selects the file to be sent to the calculator

[Receive]

selects the file to which the data received from the calculator is saved

[Stop]

closes the file

Printer

The printed text is saved to the file selected with the [Receive] button of the communication utility.

Floppy disk drive

Emulated is the MD-120 device. Files are stored in the path specified in the INI file. Error messages may be inaccurate because Delphi's file management routines do not provide a detailed cause of failure. The following disk commands are excluded: DSKF, FORMAT, MODE 200, MODE 201.

Cassette tape recorder

Not supported yet.

Integrated debugger

Disassembly box

• On entry, the starting address matches the Program Counter, but it can be modified by clicking on the address in the first line. New value must be confirmed with Enter.
• After clicking on a disassembled instruction, a new instruction can be typed. As with the starting address, pressing Enter accepts the changes. Only changes in the RAM area will be saved upon program termination, all ROM modifications will be lost. Characteristics:
  - labels and expressions aren't supported
  - accepted are hexadecimal (with the prefix &H) and decimal numbers
  - destination of relative jumps can be only specified as absolute address, not as displacement

Hex Editor box

• The HEX box allows viewing/changing the RAM contents only.
• It is possible to modify the starting address and the RAM contents by clicking on them. Enter accepts the changes.

Registers box

• The contents of the registers can be modified by clicking on them. Enter accepts the changes.
• The top line in the register box shows the state of the upper four bits of the Flag register. They can be modified as well.

Main register file box

• The contents of the registers can be modified by clicking on them. Enter accepts the changes.

Program execution control

• Closing the debugger windows resumes the program execution without tracing.
• Pressing the button [Run] in the Single step group box executes a single machine code instruction without servicing of the interrupts.
• To execute a specified number of machine code instructions type the required value to the field in the Number of steps group box, then press the associated [Run] button.
• The Breakpoint group box allows to specify condition that determine when the program execution should be interrupted. Currently it only compares the Breakpoint Address typed in the field with the Program Counter. When they match, the program execution is stopped and the debugger window reappears.

The vx3.ini file

Some parameters of the emulator can be customised by editing the vx3.ini file with any text editor.
Description of the contents of this file:

OscFreq = 910

This setting specifies the emulated CPU clock frequency in kHz.

Path = disk0

This setting specifies the path to the disk folder that stores the contents of the floppy disk. It can be relative or absolute. It can also be the name of the real floppy disk drive which allows to exchange files with a real MD-120 device (the PC and MD-120 have the same disk format if the MD-120 dip-switches are set to 2DD 720K).

Uninstalling

To uninstall the emulator, simply delete the directory where it was installed. The program doesn't modify anything outside its installation directory.

Acknowledgments

• The program includes a freeware component ThreadedTimer developed by Carlos Barbosa.

Known limitations and issues of the current version

• The sound isn't supported.
• The scrolling function of the LCD controller command $8 isn't supported.
• Bugs may still lurk in the rom0.bin memory image.