Toshiba HX-21
This page was last modified 09:46, 28 April 2020 by Mars2000you. Based on work by Rderooy and Gdx.
Toshiba HX-21.jpg




The HX-21 is an improved version of the HX-20 computer as it comes with a RGB output connector. It is an intermediate machine between the HX-20 and the HX-22.

The first serie of manufactured HX-21 computers comes with the special chipset TCX-1010 while the last has a label indicating HX-21F and comes with the special chipset TCX-1012.

As for many machines with the "Pasopia IQ" label, the PSG sound output is stereo, with a switch at the back.

Although it's a MSX1 computer, it can use a part of the MSX memory to create a RAM-Disk or Memory Disk (feature generally reserved for for MSX2 and higher computers).

As option, a RS-232C interface with switch can be added. This computer was aimed at the Japanese market.

Brand Toshiba
Type HX-21
Year 1984-10-16
Region Japan
Original price ¥79,800
RAM 64kB in slot 3-0
Media MSX cartridges
Video Texas Instruments TMS9928A
Audio PSG (AY-3-8910A)
Chipset Toshiba TCX-1010 in HX-21, Toshiba TCX-1012 in HX-21F
Extras firmware (Japanese Word Processor), MemoryDisk BASIC, (optional) RS-232C interface + switch + RS-232C BASIC, Printer BASIC, stereo PSG sound
Emulation ROMs dumped and emulated


The built-in firmware is the Japanese Word Processor, that is also available on the other Japanese computers of the HX-2x serie. It's the same version as on the HX-S501 cartridge.

From BASIC, the firmware can be launched with CALL JWP or _JWP. It includes the additional BASIC commands for Memory Disk, 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-21
Toshiba HX-21 right side
Toshiba HX-21 back
Toshiba HX-21 computer, manuals, cables and joystick (the red joystick is a Sony JS-33, the black and turquoise joystick is a Toshiba HX-J401)
Toshiba HX-21 inside
Toshiba HX-21F inside
Toshiba HX-21F label
Toshiba HX-21 box


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


The HX-21 is a MSX1 with 2 cartridge slots (one at the top, one at the back) and a a Z80A from Sharp (LH-0080A). The 64kB RAM is fully installed in slot 3-0 instead of being divided between slots 0 and 3-0.

The 2 joystick ports are located on the right side of the computer, as well as the data recorder connector.

Slot Map

Slot 0 Slot 1 Slot 2 Slot 3-0 Slot 3-1 Slot 3-2 Slot 3-3
Page C000h~FFFFh Cartridge
Slot 1
Slot 2
Page 8000h~BFFFh Firmware
Page 4000h~7FFFh Main-ROM
Page 0000h~3FFFh Mirror
  • The Firmware ROM is a 32kB ROM - 4000h-BFFFh, which is mirrored (4000h-7FFFh is mirrored to C000h-FFFFh and 8000h-BFFFh is mirrored to 0000h-3FFFh)


External links