Toshiba HX-23
This page was last modified 11:22, 18 December 2021 by Mars2000you. Based on work by Rderooy and Gdx and others.




The HX-23 is the first MSX2 computer released by Toshiba for the Japanese market with the "Pasopia IQ" label and as option a RS-232C interface with switch.

The PSG sound output is stereo, with a switch at the back.

The VRAM is limited to 64kb, what makes impossible to use SCREEN 7 and 8.

This computer was aimed at the Japanese market.

Brand Toshiba
Model HX-23
Year 1985
Region Japan
Launch price ¥98,000
RAM 64kB split between slots 0 and 3-0
Media MSX cartridges
Video Yamaha V9938
Audio PSG (AY-3-8910A)
Chipset Toshiba TCX-1012
Keyboard layout QWERTY/JIS
Extras firmware (Japanese Word Processor - Kanji-Kun v.2.5), Printer BASIC, stereo PSG sound, RS-232C BASIC, (optional) Toshiba HX-R701 RS-232C interface + switch
Emulation System is emulated based on HX-23F ROM dumps. Validation is needed that they are indeed the same. See this thread for details


The built-in firmware is version 2.5 of the Japanese Word Processor, that is also available on the other Japanese computers of the HX-2x serie. From BASIC, the firmware can be launched with CALL JWP or _JWP. It includes the additionnal BASIC instructions for RS-232C and printer.

However, you need to have the HX-M200 Kanji-ROM Level 1 in one of the cartridge slots. Note that the corresponding machine in the blueMSX emulator includes this cartridge.

It is possible to use other Kanji Roms, but if you use the Sony HBI-K16 Kanji-ROM Level 1, CALL JWP leads to a I/O device error. To bypass this problem, an addendum to the manual of the Sony cartridge gives the solution:

10 FOR I = &H9080 TO &H9120 : POKE I, &HC9 : NEXT I

The main menu includes 6 options:

  • Japanese Word Processor - if you press twice on ESC, you can access many WP features
  • Conversion Tools
  • Load and Save
  • Printer Settings and Print
  • Full Book Deletion
  • Tools for Idioms and Short Sentences

CTRL+STOP can be used to go back to the previous menu or the main menu, except if you are in the first option. You need to reboot to quit the Japanese Word Processor.



Toshiba HX-23
Toshiba HX-23 box
Toshiba HX-23 / HX-23F manuals


Toshiba JWP 2.5 - Intro screen
Toshiba JWP 2.5 - Menu
Toshiba Japanese Word Processor
Toshiba JWP - Screen after ESC key
Toshiba JWP - Conversion Tools
Toshiba JWP - Load and Save
Toshiba JWP - Printer settings (A)
Toshiba JWP - Printer settings (B)
Toshiba JWP - Full Book Deletion
Toshiba JWP - Idioms + Short Sentences


The HX-23 is a MSX2 with 2 cartridge slots (one at the top, one at the back) and a a Z80A from Sharp (LH-0080A). The 2 joystick ports are located on the right side of the computer, as well as the data recorder connector. As the VRAM size is only 64kB, SCREEN 7 and 8 can't be used.

The 64kB RAM is split in half between the slots 0 and 3-0, a configuration that can cause poorly written software to crash. Also, with this layout, the POKE-1,(15-PEEK(-1)\16)*17 trick to workaround buggy software that does not handle subslots properly will not work on this machine.

Slot Map

Slot 0 Slot 1 Slot 2 Slot 3-0 Slot 3-1 Slot 3-2 Slot 3-3
Page C000h~FFFFh Upper
32k RAM
Slot 1
Slot 2
Page 8000h~BFFFh JWP 2 JWP 1
Page 4000h~7FFFh Main-ROM Lower
32k RAM
Page 0000h~3FFFh Sub-ROM