This page was last modified 13:45, 7 December 2021 by Mars2000you. Based on work by Gdx and FiXato and others.

GR8BIT full assembled


What is GR8Bit

The GR8BIT (pronounced: 'great bit') is a Do it yourself kit (also called platform), to be assembled into the complete 8-bit MSX2/2+ computer using comprehensive set of the documentation, help of the community and support of the vendor. When developing the kit, special emphasis had been put onto the following values:

  • Larger size of the boards (main board is ATX 12" x 9.6"), DIP packages for ICs - for easy assembly;
  • Bigger number of components with least integration possible - in order for user to be able to troubleshoot/research system and electrical and logical processes within it at the detailed level, for example MSX-Engine was built on discrete components allowing easy understanding of memory and other device management;
  • Various technologies involved: Z80's Von Neumann architecture for CPU, Microchip's MCU's Harvard architecture for keyboard controller and storage subsystem controller; SRAMs for main and video memories;
  • Modularity - system comprising of a set of blocks communicating with each other, with possibility to install own developed prototypes into the system bus (called GR8BUS, uses standard 62-pin ISA edge connector);
  • Proper licensing from technology owners - kit contains license to use its platform-related Intellectual property, as well as IP of the MSX Licensing Corporation;
  • Comprehensive documentation - aim is not only educating how to build the system, but also on how it operates.


Specifications table is continuously updated as more and more devices are being certified for the platform.

Compatibility MSX2 standard (fully compatible)
MSX2+ standard (partially compatible, full compatibility requires V9958)
ATX form factor
Power management ATX power management compliant
Software power off function
CPU Z80 (4-20MHz), compatible or emulation board (3.3V)
Multi-processor capable
Main system memory 1MiB (SRAM), upgradeable to 4MiB
Further extensions to 1GiB (DRAM)
Video subsystem V9938 VDP, 128KiB VRAM, direct video memory access
Composite TV output (grayscale), RGB NTSC output
Storage interfaces 1.44MiB FDD: «Standard» (1 sectors/cluster, 9 FAT sectors) and «Compatible» (4 sectors/cluster, 3 FAT sectors)
Any compatible storage device in the external slots
Input interfaces PS/2 keyboard interface (requires keyboard controller installed)
Compatible keyboard interface
I/O ports and interfaces 7 GR8BUS internal slots
2 expandable external slots (1 and 2)
2 GR8BUS adaptor boards for internal cartridge connection
Advanced printer port / parallel datacomm port
2 compatible joystick ports / general I/O ports
Multimedia capabilities 3 channel programmable sound generator
Tunable square waveform generator
Additional 5 programmable channels when using SCC
8-bit Covox in parallel port
Networking capabilities (No certified devices yet)
Software Language pack (replacement for Kanji ROM, 16KiB). Languages: JA, EN, RU, ES, FR, DE.
Gaming (list, database, more than 320 titles)
Software development (ASCII C, ASCII Assembler, BASIC, Fortran, Cobol, whatever, database)
ROM images (database)
Operating systems (MSX-DOS, CP/M, SymbOs)
Emulation (BlueMSX, OpenMSX)

The Basics

GR8BIT can be seen as a hardware platform, however, being an MSX-standard compliant device, it runs MSX software, such as games, MSX-DOS, compilers for C, Pascal, Fortran and Z80 assembler. With PIC MCUs added, it also provides option to code microcontroller versions of C and assembler.


The set of documentation consists of the set of books, called GR8BOOKs:

  • Part I: Principles of Operation;
  • Part II: Assembling your GR8BIT;
  • Part III: Starting and booting your GR8BIT;
  • Part IV: Component reference;
  • Part V: Circuit diagrams, PCB layouts and pin-outs;

There were two books added to this set:

  • Part VI: Additional devices; and
  • Part VII: Discontinued designs.


There're three types of licenses utilized within the kit:

  • GR8BIT license - for usage of the circuit diagrams, documentation and support;
  • MSX license - for usage of the MSX software with GR8BIT as well as within emulation software like blueMSX or openMSX;
  • Copyleft for software and specific IP - firmware for system components, application software, configuration modules (Verilog) for GR8BUS master board and schematics libraries to create custom boards for the platform.


The kit itself (called GR8BOX) comprises of almost all components, including PCBs, resistors, capacitors, integrated circuits, connectors et al. User will only need components like ATX chassis (with Power supply), floppy and Parallel ATA hard drive(s), PS/2 keyboard and TV to operate assembled system.

Physical properties of the kit

Due to the kit not including ATX box, hard drive, floppy drive and other big components (which can be obtained from decommissioned PC systems locally), the size of the GR8BOX is as small as 25 x 27 x 6.6 cm, and weight is about 1.65 kg.

GR8BIT Box opened
GR8BIT Box opened

CPU Board

GR8BIT CPU board

External Slots

External slots must be connected on the expansion BUS of the slot board.

GR8BIT Slot board
GR8BIT External slots board

I/O board

GR8BIT I/O board v1
GR8BIT I/O board v2

Keyboard Interface

There're two types of the keyboards can be attached to the machine - PS/2 keyboard or standard MSX keyboard device (Yamaha/Daewoo/Sony). You may have both attached at one time, but MSX keyboard will work only when PS/2 keyboard controller is suspended (F12 key).

Main Board

GR8BIT main board v1
GR8BIT main board v2

Memory Board

Memory board by default has 1Megabyte of the mapped SRAM memory. It has large development area to solder additional components or memory chips.

GR8BIT Memory board

Video Board

GR8BIT Video board v1
GR8BIT Video board v2

GR8BUS Master Board

GR8BUS Master Board is composed of 32MB RAM, a FPGA and I/O programmable, and a stereo sound output. By default the FPGA is programmed to reproduce the SCC sound and 5 independant DACs as COVOX (PCM). It is sold separately.

GR8BUS Master Board
GR8BUS Master Board back

External links

GR8BIT™, GR8BOOK™, GR8BUS™ and GR8BOX™ are trade marks copyright © 2010-2011 Eugeny Brychkov.
All other trademarks and copyrights are the property of their respective owners.

GR8Bit Wiki started by Erik Luppes based on a Creative Commons 4.0 International-license.
Original at