Category:Sony HB-20
This page was last modified 01:51, 18 January 2021 by Mars2000you.



The Sony HB-20 is a computer that was released only in Spain, it exists in 2 versions, both have a black case.

  • The HB-20P (P for PAL) is the same machine as the HB-10P, missing only the DIN5 video monitor connector. The power supply is the external Sony AC-HB2P.
  • The HB-20N seems to be the same machine as the HB-20P, except for little details such as colored keys. The power supply is the external Sony AC-HB1P. We don't have info about the inside of the machine, so the table below is probably incorrect for the HB-20N.
Brand Sony
Model HB-20N / HB-20P
Year 1986
Region Spain
Launch price
RAM 64kB in slot 3
Media Cartridges
Video Toshiba T6950A
Audio PSG (YM2149 integrated in MSX-Engine S3527)
Chipset Yamaha S3527
Keyboard layout QWERTY with a "ñ" key
Emulation ROM dumped and emulated for HB-20P versions. ROM dumps needed for the HB-20N version. See this thread for details


Sony HB-20N
Sony HB-20P
Sony HB-20P motherboard with video daughterboard
Sony HB-20P normal motherboard
Sony HB-20P/N back
Sony HB-20P video board


Note: Details are missing about the HB-20N, the infos below are verified only for the HB-20P.

The HB-20 is a MSX1 with a Z80A from NEC (DA780C-1) or Sharp (LH0080A). The MSX-Engine comes from Yamaha (S3527).

The VDP is the Toshiba T6950A, which does not support some undocumented features of the Texas Instruments TMS9918, TMS9928 and TMS9929 VDP's.

One of the machine pictures above include a video daughterboard with the VDP, the VRAMs and some glue logic. It's intended to allow a different type of VRAM type to be used, either PSRAM or SRAM, since the motherboard only accepts 4116 DRAMs. Only some batches of HP-20P feature this daughterboard, while the majority has the T6950A VDP and 4116 DRAMs directly installed on the motherboard. This daughterboard causes absolutely no perceptible changes from the software point of view.

Slot Map for the HB-20P

Slot 0 Slot 1 Slot 2 Slot 3
Page C000h~FFFFh RAM mirror* Cartridge
Slot 1
Slot 2
Page 8000h~BFFFh
Page 4000h~7FFFh Main-ROM
Page 0000h~3FFFh

(*) RAM mirror quirk on early models


Quirk on port A8h

Just like the HB-10P computer, some early versions of the HB-20P also have a quirk on port A8h that makes RAM bank 3 appear mirrored both in slot 0 and in slot 3. This effect is emulated in openMSX for the Sony HB-10P, it can cause problems with bugged software have trouble running on split-RAM configurations, making them crash.

Nevertheless, you can run these games if you type the following command before loading:

OUT &hA8,240

For cartridges, the trick is to plug them in after booting the MSX using a slot expander that has switches to disable each slot and prevent them from auto booting (WARNING!! Do not insert a cartridge when power is ON. It can damage the machine). Then type the following instructions on BASIC after re-enabling the slot:

OUT&hA8,240: DEFUSR=&H7D75: ?USR(0)

Alternatively, you can use ROM loaders like Execrom, LoadROM or OPFX /X. Since they start the game from MSX-DOS, this problem will be automatically solved as DOS already selects the correct slots for the RAM.

Fixes, Repair and Upgrades

Pages in category "Sony HB-20"

The following 2 pages are in this category, out of 2 total.