Game Boy Software Development Kits

Edit on Github | Updated: 11th January 2020

Official GameBoy Software Development Kit (by Intelligent Systems)

The official Game Boy development kit was developed by Intelligent systems and sold with their development kit hardware such as the DMG-ICE. It evolved over time and added support for the Gameboy Color, eventually becoming the SDK shipped with the IS-CGB-EMULATOR hardware.

Gameboy (DMG & GBC) Development Kit Hardware

For more information on the development hardware check out this post.

Using the SDK

If you are interested in using the SDK to develop homebrew or to help reverse engineer a game that used the Official SDK then this section will guide you through some of the basics.

Download the Official Game Boy Color SDK

You can download the Japanese version of the Gameboy Color SDK from emuparadise here: Gameboy Color SDK


The official manual for the Software Development Kit was uploaded to and is available here: Gameboy Development Manual V1.1 : Nintendo : Free Download, Borrow, and Streaming : Internet Archive

Tools included

Intelligent Systems Assembler (ISAS)

To assemble your GameBoy source code into Z80 machine code you could use the official Nintendo (Intelligent Systems) assembler and linker, ISAS and ISLK respectively. Last Known Version: ISAS 1.26 / ISLK 1.26 (1999/10/26)

Intelligent Systems eXecutable - ISX and CVTISX

ISX is the format that the Assembler (ISAS) compiles the programs into, it is a compressed version of the rom, to convert it into a standard gameboy rom you need to run it through CVTISX (ConvertISX).

Intelligent Systems Character Designer (IS-CGB-CAD or DMG-CAD)

The archive only seems to contains the IS-CGB-CAD tool, which I presume is some sort of graphics/map editor. Graphics, Sprites and Tiles are known as “characters” for the GameBoy. Its known as a Character development system. So I presume it stands for Intelligent Systems Character A??? Designer or Development


Just before the Intelligent Systems development FTP server was shut down, someone managed to backup the contents of the Gameboy color sdk and the files that were saved are as follows:

  • IS-CGB-SDK.7z - Software development kit (libraries etc)
  • IS-CGB-EMULATOR.7z - Color Gameboy Emulator
  • IS-CGB-DEBUGGER.7z - Gameboy debugger
  • IS-CGB-CAD.7z - Character/Graphics development tool
  • IS-CGB-CHARACTER.7z - Character/Graphics development tool
  • IS-CGB-CHARACTER Documentation.7z - Documentation for the CAD graphics tool

Original Game Boy DMG SDK (Contained in Gigaleak archive called Other.7z)

In the first Nintendo Gigaleak the source code for the original Zelda Links Awakening for the DMG Game Boy was included which contained what is believed to be the full Software Development Kit used both in-house at Nintendo and a few partners such as Systems Research and Development (SRD).

The files included in the Original DMG SDK are described in the table below:

File Name Extension Description
A .EXE DMG Relocatable Macro Assembler Version 1.00
ASMB .EXE 6502 Assembler Version 1.10 (Famicom tool created in 1987)
ASMD .EXE DMG Macro Assembler Version 1.01
ASMDMG .EXE DMG Macro Assembler Version 1.01 (Identical to ASMD.EXE)
CGE2DMG .EXE Converts either CGE or DCG Character graphics to source code (.DMG)
CGEDCG .BAT Batch file for running FCV with the DCG2BYT script
DCG2BYT .CVT FCV Script to convert DCG Character Graphics files to assembly code (.DMG)
DCGDMG .BAT Batch file for character file conversion of a .DCG file to a .DMG source file
DMGFUNC .TB0 Custom binary format possibly used by ISD debugger tool contains the string “SENGOKU” at the start
FCV .EXE File Convert Program Version 1.03 (Reads in .CVT files)
FDT .EXE FMS Debugger Version 2.02 (Famicom Tool?)
GENBYTE .CVT FCV Script to convert a .COM file to a NES/SNES .X65 source file
HDT .EXE MMC/HVC Debugger Version 03.05 (Famicom/NES Dubugger)
IS65 .EXE 6502,65816 Relocatable Macro Assembler version 1.00 (Why is there a SNES assembler in here?)
ISD .EXE I.S. Debugger Version 1.00c
ISDMG .EXE DMG Relocatable Macro Assembler Version 1.00
ISLINK .EXE ISASM Linker Version 1.00
L .EXE ISASM Linker Version 1.00 (Presumably just copied to have a shorter name)
PW .EXE P-ROM Support Program Version 1.26
PW2 .EXE, .TB0 P-ROM Support Program Version 2.02d6
SCR2DMG .COM MS-DOS Command File Executable for converting .scr files to .DMG files for assembling
SHL .COM, .KEY MS-DOS Command File Executable but not sure what it is for
SHVC .EXE SHVC Debugger Version 1.00a
VRAMTR .CVT VRAM Transfer script that converts a .SCR screen file to either a NES or SNES .X65 file
VUP .EXE Version UP Program Version 2.09

Game Boy SDK File Formats

This SDK seems to use a number of different file formats, but it is not clear what exactly is the purpose of each:

  • .DMG - Assembly source code for the Dot Matrix Game (Game Boy)
  • .CGE - Character Graphics data (For famicom?)
  • .DCG - Character Graphics data (for DMG Game Boy?)
  • .CVT - Custom Conversion scripts that can be executed with FCV
  • .SCR - Screen file maybe containing location of character tiles in a level?
  • .X65 - Either Famicom or Super Famicom source code
  • .COM - Unsure if this is a Windows Command File or something else

NES/Famicom SDK Files

One interesting file is that HDT.EXE is included here which is the NES/Famicom Debugger, as far as I know this is the first time a file from the Famicom SDK has ever been leaked. As no other official NES/Famicom SDK had been leaked this is quite remarkable. It was written by Intelligent Systems between 1986-1989 and seems to read in three file formats: CHR (Character/Tile Data), SCR (Screen data? or Source Data?) and CGD (No Idea, maybe Character Graphic Designer?).

SNES/Super Famicom SDK Files

Another interesting file is that IS65.EXE is included here which is the Official Super Nintendo Entertainment System assembler created by Intelligent Systems in 1990. It seems to have been written by the developer Toshio Sengoku.

The file VRAMTR.CVT which is a script in a custom programming langauge that is parsed by the FCV program. The comments at the beginning of the file indicate that it takes an input file with a “.SCR” extension and outputs a file with a “.X65” extension.

File Convert Program

The File Convert Program (FCV) tool was created in 1987 by Intelligent Systems so it is likely it was also part of the Famicom Software Development Kit.

The commands in the script appear to be performing various operations related to transferring data to VRAM. For example, the “VRAD=$2000” command sets the screen address, and the “DTPT=0” command initializes the data pointer. The script also includes commands for writing screen data and attribute data to VRAM.

Character Graphics conversion

The Bash script DCGDMG.BAT is used to convert a file with the extension “.DCG” (presumably containing character graphics) from the FM-R50 system (a Japanese computer system from the 80s) to a source code file with the extension “.DMG”.

The script assumes that the FM-R50 file is inserted into Drive A of the computer. The script then uses the FCV tool to do the conversion.

This potentially means that developers for Nintendo were using the Fujitsu FM-R50 or a compatible system to develop Game Boy games and possibly NES and SNES games too.

Third Party SDKs

Many third party game developers to create their own set of development libraries and even assemblers, emulators and debuggers to make Gameboy development easier.

AZ40 Gameboy Assembler Kit (Gremlin)

This is a very old Gameboy assembler kit created around 1991 by Gremlin Graphics Software. Included in the kit the assembler, macros, debugger and Amiga to Gameboy sample converter, Gameboy file clipper, set memory application and a restart application 1.

The SDK can be downloaded from - Utilities - AZ40 GameBoy Assembler Kit.

Executables included

There are a few executables that can be used in DOS for assembling, debugging and a few sound tools.

Name Description
AZ40.EXE Gameboy Assembler (Gameboy Esprit Turbo Assembler)
DZ40.EXE Gameboy Debugger (Copyright 1991 Gremlin Graphics Software Ltd.)
RESTART.EXE Seems to connect to a gameboy (to restart it?)

Along with the release on there was another release of Gameboy source code that included it in a zip file called It seems to have the source code for the music for the amiga game called “The Humans” along with gameboy specific source code and the SDK.

Unanswered questions

Who or what was R.H.C?

In the Gremlin SDK it mentions that a lot of tools were by R.H.C, but it is unclear who or what this is. It could be the initials of an employee who wrote the software or it could be a company. They seem to have written both ATG.EXE and CUTFILE.EXE.

R.H.C was possibly Richard Hutchison as that was a college of Barry and worked on a few titles together, but this is unconfirmed? 2.