Neos MA-20
This page was last modified 18:11, 7 June 2021 by Mars2000you. Based on work by Gdx and Rderooy 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. Compatibility with MSX1 hardware and MSX2 software can be found here.

Brand Neos
Model MA-20
Year 1986
Region Japan
Launch price ¥29,800
RAM at least 64kB on the MSX1 host
VRAM 128kB
Media MSX cartridges, possibly 1DD or 2DD floppy disks or cassette tapes (from the MSX1 host)
Video Yamaha V9938
Audio PSG (from the MSX1 host)
Chipset possibly on MSX1 host
Keyboard layout keyboard of the 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