Toshiba HX-23
This page was last modified 09:24, 6 March 2018 by Gdx. Based on work by Mars2000you and Rderooy 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.

Official price: ¥98,000

Brand Toshiba
Type HX-23
Year 1985
RAM 64kB split between slots 0 and 3-0
Media MSX cartridges
Video Yamaha V9938
Audio PSG (AY-3-8910A)
Chipset Toshiba TCX-1012
Extras firmware (Japanese Word Processor), stereo PSG sound, Printer BASIC, (optional) RS-232C interface + switch + RS-232C BASIC


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 commands 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



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


Toshiba Japanese Word Processor
Toshiba Japanese Word Processor
Toshiba Japanese Word Processor
Toshiba Japanese Word Processor
Toshiba Japanese Word Processor


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
Bank C000h~FFFFh RAM Cartridge
Slot 1
Slot 2
Bank 8000h~BFFFh JWP 2 JWP 1
Bank 4000h~7FFFh Main-ROM RAM
Bank 0000h~3FFFh Sub-ROM