Neos MA-20
This page was last modified 15:05, 29 January 2020 by Rderooy. Based on work by Gdx and Syn and others.



The Neos MA-20 "Version Up Adapter" has been released in 1986 in Japan. The packaging contains two cartridges - Neos MA-20(V) and Neos MA-20(R) - to upgrade a MSX1 to MSX2:

  • The big cartridge Neos MA-20(V) contains a V9938 VDP, 128kB VRAM and a ROM that includes the MSX2 sub-ROM (or extension ROM) and MSX-DOS initialization software
  • The smaller cartridge Neos MA-20(R) contains the new main ROM (Bios + Basic v2.0) and the clock chip, it must be inserted into a lower slot

The MA-20 requires a MSX1 with 64kB RAM and two slots. Most MSX2 games that do not access directly the VDP work with this adapter.

Brand Neos
Type MA-20
Year 1986
Region Japan
Original price ¥29,800
RAM at least 64kB on the MSX1 host
VRAM 128kB
Media MSX cartridges, eventually 1DD or 2DD floppy disks or cassette tapes (from the MSX1 host)
Video Yamaha V9938
Audio PSG (from the MSX1 host)
Chipset eventually on MSX1 host
Emulation ROMs dumped and emulated


Neos MA-20(V)
Neos MA-20(V) PCB underside
Neos MA-20(V) PCB
Neos MA-20(R)
Neos MA-20 box and cartridges
Neos MA-20 manual and cartridges
Neos MA-20(V) back


The MSX2 'added' to the MSX1 is a computer that depends from the MSX1 host for some of its features, especially the PSG, the available RAM and the usable media. The real time clock has a standard I/O address. Used I/O ports for the VDP are #88~#8B.


  • RF output
  • RGB output
  • Analog sound input
  • Composite video output


Hardware Compatibility

There are a few compatibility problems with some computers, for example the Daewoo DPC-200 (probably a conflict with the Hangul driver ROM) or the Yamaha CX5MII and CX5MII/128 (have an incompatible rom which uses hooks to expand the screen width to 80 columns).

It is meaningless to use this adapter on a MSX2 or higher machine, but if you try that, it will not work on MSX2 or MSX2+, but will on Turbo R:

  • the MA-20 does not work with a MSX2 or MSX2+, because the initializiation routines search for any subrom in any slot. Therefore it calls the subrom of the MA-20 without proper V9938 initialization, which causes the subrom to hang.
  • the reason it is working in a Turbo R is because this machine does not search for a subrom, the slot id of the subrom is hardcoded in the initialization code. Therefore the subrom of the MA-20 is called after the MA-20 mainrom is initialized which works just fine.

Software Compatibility

The MA-20 replaces the internal BIOS with a specific Japanese BIOS. Several keys will return bad characters on an non-Japanese MSX. In addition, the standard MSX1 specification states that the BIOS must be in slot 0 or 0-0 which will not be the case, for these reasons and a few others it is better to remove the cartridge to run MSX1 software.

Unsupported MSX2 software list:

The games below seem to work although direct access to the VDP seems to occur at least once.

Note : The list is non-exhaustive.