This page was last modified 12:51, 10 June 2022 by Gdx. Based on work by Sylvester and Mars2000you and others.



GR8NET is a combo cartridge for MSX with Network as its main function. It has 8 distinctive mapper modes, 7 composite mapper modes and a very extended MSX-BASIC add-on (see GR8NET BASIC). It can be used on any MSX generation.

Since serial number 056C, GR8NET has a native stereo out using 3.5 mm jack, and a side switch to disconnect GR8NET output from the internal MSX mixer, therefore GR8NET's output appears on the 3.5 mm jack output, and all other devices installed into machine will sound through machine's audio output.

Since serial number 05BD, GR8NET comes with a 16MB serial flash chip, earlier GR8NETs have only a 2MB serial flash chip, but they can be upgraded with 16 MB chip.

GR8NET has SD-card interface accessible through internal _NET instructions (FAT16/FAT32/exFAT) and through Nextor (in composite mapper modes - FAT12/FAT16); several multimedia devices - MSX-MUSIC, MSX-AUDIO, OPL4, PSG and SCC. It can operate in MP3 media player mode playing MP3 files from network, SD-card, or online streams (internet radio).

The cartridge operates in primary slot (all mapper modes) and sub-slot (except all composite mapper modes when slot expansion is performed internally), in all MSX models.

GR8NET developer, Eugeny Brychkov, is also developer of a platform called GR8BIT. You can find infos and docs about GR8NET on the GR8BIT site:


Audiophile GR8NET packaging
GR8NET with manual printed from the pdf
GR8NET top
GR8NET back


  • Flash card:1 slot compatible with micro SD and micro SDHC cards (32-bit sector addressing, max addressable space of 2 TB)
    • Supports hot card swap
    • Maximum partition size of 4GB (FAT16), maximal card size (FAT32/exFAT)
    • Uses Nextor as DOS (native FAT12/16 support) or _NET instructions (FAT16/FAT32/exFAT)
    • High speed transfer (read and write)
  • RAM: 1024K
    • Depending on the mapper type selected mapped RAM may be of 1024K size, or half of 512K, or be completely disabled. In two latter cases unused RAM may be used for another purposes (e.g. game mapper).
    • Mappers emulation: Plain 32K/64K, mapper for Network, ASCII 8/16K, Konami without SCC, Konami SCC+, memory mapper, mixed half for Network and half memory mapper, composite mappers, MegaRAM
    • RAM-disk 2KB to 720kB, user programmable size
  • 512K flash for firmware (GR8NET ROM BIOS), Nextor Kernel, etc
  • 2MB / 16MB of serial flash chip storage, which may contain:
    • FPGA images (engines - regular, MP3, OPL4)
    • ROM catalogs (sets of compressed ROMs organized as catalog accessible using _NETBROWSE)
    • Kanji-ROM (256Kb)
    • YRW801 OPL4 ROM images - original 12-bit (for 16MB flash devices), or 8-bit (for 2MB flash devices)
  • Network
    • RJ-45 UTP Ethernet connection, 10/100 Mbit auto-negotiation / auto MDI, IPv4
    • TCP, UDP, RAW and HTTP communication protocols, including using standard BASIC file I/O instructions (OPEN, CLOSE INPUT, PRINT, EOF, etc)
    • Built-in simple web browser to browse web server directory tree (_NETBROWSE)
    • DHCP configuration, DNS auto-resolution, time synchronization (using NTP)
    • 3 user programmable sockets
    • MSX-BASIC extended instructions
    • Built-in terminal and telnet application (SCREEN 5)
    • Built-in HTTP-based bload application (_NETBLOAD)
    • TCP/IP UNAPI version 1.0 implementation
    • GR8cloud virtual volume through Nextor in composite mapper modes
  • Sound
    • Native stereo output since serial number 6C for internal emulated sound chips
    • PSG emulation at standard ports (PSG cloning), can be reconfigured to I/O ports 10h-12h
    • Konami SCC and SCC+ emulation
    • Emulated OPLL (YM2413, MSX-MUSIC) with its ROM BIOS (in mapper mode 8)
    • Emulated OPL1 with ADPCM (Y8950, MSX-AUDIO), including MSX-Audio BIOS
    • OPL4 with standard 12-bit sample ROM for 16 MB serial flash devices, and 8-bit sample ROM for 2 MB serial flash devices
    • PCM buffered 8- and 16-bit mono and stereo performance
    • MP3 audio streaming from network and SD-card (44.1/48 kHz, auto-selectable)
    • Internal mixer configurable for tuning volume of internal sound sources and even the stereo out. Logarithmic scale
  • Display
    • Kanji-ROM JIS1 + JIS2, selectable from one of 5 font sets (Only one image can be active at a time, however serial flash may hold more than one image, switching can be performed by _NETKJROM instruction):
    • Video player
      • SCREEN 2 mode: 256*192 with ~12 fps
      • SCREEN 8 or 12: resolution and fps factors are selected from the matrix (136x102 @ 12 fps ... 256x192 @ 3.3 fps)
      • Audio is mono 22 kHz, 8 bit
      • Video size (playback duration) is only limited by the file system
  • Misc
    • MSX-BASIC Kun Turbo / X-BASIC (2.1) support
    • Interrupt generator using time period or frequency, with watchdog
    • Mathpack for FAT16/FAT32 and 32-bit multiplication and division (fast calculation)
    • Data prefetch (indirect access) from onboard RAM, ROM and W5100
    • Mixed 512kB GR8NET mapper and 512kB memory mapper mode supports Nextor with SDC
    • Operates at standard 3.58 MHz as well as at overclocked 7.11 MHz bus speeds
    • Konami sized cartridge

Mapper modes

Number Mode
1 Plain 32kB ROM
2 Konami without SCC (K4)
3 Konami with SCC (K5)
5 ASCII 16
6 Mirrored ROM
7 1MB mapped RAM
8 Composite with MSX-MUSIC BIOS and SCC(+) in subslot 3
9 Composite with plain 32kB ROM game mapper in subslot 3
10 Composite with Konami without SCC (K4) game mapper in subslot 3
11 Composite with Konami with SCC (K5) game mapper in subslot 3
12 Composite with ASCII 8 game mapper in subslot 3
13 Composite with ASCII 16 game mapper in subslot 3
14 Composite with mirrored rom game mapper in subslot 3
15 Not valid mode

Composite mapper modes

In these mapper modes GR8NET performs internal slot expansion, thus it must be installed into primary slot.

  • In mapper mode 8 subslot 0 is having GR8NET mapper, subslot 1 is having 512kB mapped RAM, subslot 2 is having Nextor driving SD-card and GRcloud virtual volume, and subtlot 3 is having MSX-MUSIC BIOS;
  • In mapper modes 9-14 substlots 0-2 are having identical allocation as for mapper mode 8, but subslot 3 is having respective game mapper from the list with values 1 to 6.
  • Mapper mode 15 is not valid.


  1. In mapper modes 9-14 game mappers share space with GR8NET mapper, while game mappers are read-only for applications running within them, the contents of ROM can be changed (or corrupt) through GR8NET mapper - for example by using RAM disk;
  2. Mapped RAM can be disabled for composite mappers (some games/applications will not work properly if machine's main RAM is in same slot as game mapper);
  3. MSX-Audio BIOS can be switched on instead of mapped RAM;
  4. Nextor can be disabled.

Minimum System Requirements

  • MSX computer with one free primary slot cartridge connector (all mapper modes / OPL4)
  • MSX computer with one free secondary slot cartridge connector (e.g. slot expander - mapper modes 0-7 / OPL4)