Nintendo Game Boy Link Cable Owner's manual

DMG-06-4216-001-B
Released 12/03/1999
PROGRAMMING MANUAL
Version 1.1

“Confidential”
This document contains confidential and proprietary information of
Nintendo and is also protected under the copyright laws of the United
States and foreign countries. No part of this document may be released,
distributed, transmitted or reproduced in any form or by any electronic
or mechanical means, including information storage and retrieval
systems, without permission in writing from Nintendo.
1999, 2000 Nintendo of America Inc.
TM and are trademarks of Nintendo

Introduction
3
INTRODUCTION
This manual is a combination and reorganization of the information presented in the Game Boy Development
Manual, revision G, and the Game Boy Color User's Guide, version 1.3. In addition, it incorporates all information
related to Game Boy programming, including programming for Super Game Boy and the Game Boy Pocket
Printer.
The abbreviations used in this manual represent the following:
DMG: Game Boy (monochrome), introduced on April 21, 1989
MGB: Game Boy Pocket (monochrome), introduced on July 21, 1996
MGL: Game Boy Light (monochrome), introduced on April 14, 1998
CGB: Game Boy Color (color), introduced on October 21, 1998
Note: Where it is not necessary to distinguish between the different monochrome
models, DMG is used to refer to both monochrome models, and CGB is used to
denote the Color Game Boy.Only whereit is necessaryto distinguishbetween
the monochrome models is MGB used to denote Game Boy and MGL used to
denote Game Boy Light.
SGB: Super Game Boy, introduced on June 14, 1994
SGB2: Super Game Boy 2, introduced on January 30, 1998
Note: SGB is used to denote both SGB and SGB2 when no distinction is necessary.
SGB2 is used only in cases where distinction is necessary.

Game Boy Programming Manual
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Preface: To Publishers
5
PREFACE: TO PUBLISHERS
NINTENDO GAME BOY COLOR SOFTWARE PRE-APPROVAL
REQUIREMENTS
Prior to submitting your CGB software to Lot Check for approval, it is required that you submit it to the Licensee
Product Support Group for pre-approval. To assist us with the evaluation of your CGB software and/or product
proposal(s), please refer to the following requirements when submitting materials* for approval.
* Please do not send original artwork or materials, as they will not be returned.
CGB software and/or product proposals are evaluated based on the following criteria:
•Use of Color
To ensure that the expectations of the Game Boy Color consumer are met, Mario Club will evaluate the use
of color in all CGB games (dual or dedicated) using the following criteria:
◊Differentiation - If a game is to be considered CGB-compatible, then it must appear significantly more
colorful than a monochrome Game Boy game when “colorized” by the CGB hardware. The principal
measure of this is the number of colors in the background (BG) and the number of colors in the objects
(OBJ).
◊Simultaneous Colors - Because CGB hardware automatically “colorizes” monochrome games with up
to four colors in the BG palette and up to six colors for two OBJ palettes (three colors per palette), a
game typically must display more colors than this automatic “colorization” to be considered a CGB
game.
◊Appropriate use of Color - Objects in the game that are based on reality (trees, rocks, animals, and
so on) should be a color that we would normally associate with them. For fictional objects, colors
should be chosen to show appropriate detail and, when needed, to differentiate unlike objects.
◊Variety of Colors - The CGB is capable of producing a wide range of colors (32,768 to be exact --
albeit not all at the same time). A CGB game should use this capability of the hardware to yield
distinctly different colors for objects, characters, areas, and so on.
◊Contrast & Saturation - Two of the elements that make a game look colorful are high contrast and
“saturated” or vibrant colors. Pastel colors on a white background will not seem nearly as colorful as
the same colors on a dark background. Not every game can use a dark background, but the intensity
of the colors should still be maximized as much as possible.
Please detail or demonstrate how your game will utilize color capabilities of the CGB. Use whatever means
will best allow you to do so, such as artists renderings, programmed demos, ROM images, written
descriptions, and so on.

Game Boy Programming Manual
6
•
Game Concept Content
We do not require an explanation of, or evaluate game concept content for original CGB titles. However, if
you are planning to “colorize” a previously released monochrome game we require that it include game-play
enhancements (beyond simply adding color) to differentiate it from its monochrome counterpart. Such
game-play enhancements may include, but are not limited to: additional stages, levels, or areas; new
characters; additional items; game-play based on color; and so on. These enhancements must be readily
apparent to players familiar with the original monochrome game.
Please submit a written proposal of the enhancements to us for pre-approval. Use whatever additional
means that will best allow you to communicate the game-play enhancements, such as storyboards,
treatments, videotapes, programmed demos, and so on.
•Interim ROM Submissions
We require at least one interim ROM submission to Mario Club (at approximately 50% completion) for
preliminary review of the use of color in every CGB game. By reviewing the interim ROM and providing you
with feedback in the early stages, we also help ensure that your projects stay on schedule. Final pre-
approval is based on Mario Club’s evaluation of a ROM near completion of game development.
If you wish to arrange electronic transfer of the ROMimage, please contact Terral Dunn in our Testing
and Engineering department at [phone] or by e-mail at “[e-mail]”. Please notify
him when you have made an electronic submission for our review.
•
Proposed Developer
Please supply us with the name, addressand phone number of the proposed developer. If the developer is
not an Authorized Nintendo CGB Developer, please contact Melody Morgan at “[e-mail]”or
425-861-2618, and she will provide you with the application information.
•Schedule Information
Please provide us with an estimated product schedule, including interim ROM submission(s), final Mario
Club submission, submission of the master ROM to Lot Check, and the release date.
•Game Pak Configuration & Game Type
Please provide us with the estimated Game Pak size in Megabits (Mb) and the RAM size if internal memory
is to be used to save game information. Also state whether the game will be compatible with the
monochrome Game Boy hardware or if it is dedicated to CGB hardware. For the current Game Pak prices
and configurations available, please contact Nintendo’s Licensing Department.
You will be contacted with the evaluation results when the Licensee Product Support Group has completed its
evaluation of your ROM or concept submission.

Table of Contents
7
Table of Contents
Page Number
Introduction.......................................................................................... 3
Preface: To Publishers......................................................................... 5
Chapter 1 System................................................................................. 9
Chapter 2 Display Functions............................................................. 47
Chapter 3 Sound Functions............................................................... 77
Chapter 4 CPU Instruction Set .......................................................... 93
Chapter 5 Miscellaneous General Information............................... 125
Chapter 6 The Super Game Boy System........................................ 137
Chapter 7 Super Game Boy Sound................................................. 187
Chapter 8 Game Boy Memory Controllers(MBC) ........................... 215
Chapter 9 Pocket Printer.................................................................. 235
Appendix 1 Programming Cautions................................................ 253
Appendix 2 Register and Instruction Set Summaries.................... 267
Appendix 3 Software Submission Requirements .......................... 285

Game Boy Programming Manual
8
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Chapter 1: System
9
CHAPTER 1: SYSTEM..............................................................11
Revision History…………………………………………………………….10
1. GENERAL SYSTEM ......................................................................11
1.1 System Overview.....................................................................................11
1.2 Game Boy Block Diagram.......................................................................13
1.3 Memory Configuration.............................................................................14
1.4 Memory Map.............................................................................................15
1.5 Feature Comparison................................................................................16
1.6 Register Comparison...............................................................................17
2. CPU................................................................................................18
2.1 Overview of CPU Features......................................................................18
2.2 CPU Block Diagram.................................................................................20
2.3 Description of CPU Functions................................................................22
2.4 CPU Functions (Common to DMG/CGB
➀
➀➀
➀
).............................................24
2.5 CPU Functions (Common to DMG/CBG
➁
➁➁
➁
).............................................28
2.6 CPU Functions (CGB only)......................................................................34

Game Boy Programming Manual
10
Revision History
Date Section Description
12/3/99 2.6.3 Revision of description for Infrared Communication

Chapter 1: System
11
CHAPTER 1: SYSTEM
1. GENERAL SYSTEM INFORMATION
1.1 System Overview
Structure
At the heart of the DMG/CGB system is a CPU with a built-in LCD controller designed for
DMG/CGB use.
System
Features common to DMG/CGB
!32-pin connector (for ROM cartridge connection)
!6-pin subconnector (for external serial communication)
!DC-DC converter for power source
!Sound amp
!Keys for operation
!Speaker
!Stereo headphone connector
!Input connector for external power source
Types of Game Pak Supported
1 Game Boy Game Pak
(Software that uses only the Game Boy functions. When used with Game Boy Color, 4-
10 colors are displayed.)
2 Game Boy Color Game Pak
!Game Pak supported by CGB (for use with both CGB and DMG)
!Game Pak for CGB only (software that runs only on CGB)
[DMG]
!Dot-matrix LCD unit capable of
grayscale display
!64 Kbit – SRAM (for LCD display)
!64 Kbit – SRAM (working memory)
[CGB]
!Color dot-matrix LCD unit capable of
RGB with 32 grayscale shades
!128 Kbit – SRAM (for LCD display)
!256 Kbit – SRAM (working memory)
!Infrared communication link (photo
transistor, photo LED)

Game Boy Programming Manual
12
Operating Modes (the following modes apply only to CGB)
1 DMG Mode (when using software for DMG)
The new registers, expanded memory area, and new features for CGB are not used.
Color applications previously associated with palette data BGP, OBP0, and OBP1 are
performed by the system.
2 CGB Mode (when using software supported or used exclusively by CGB )
The new registers, expanded memory area, and new features of CGB are available.
Note: To operate in CGB mode, specific code must first be placed in the ROM
data area of the user program. For more information, see Chapter 5,
Section2, Recognition Data for CGB(CGB only)in ROM-Registered Data.
Power Source
!Battery/AC adapter/Battery charger
Accessories (as of April 1999)
DMG Accessories
!Communication Cable
!Battery Charger Adapter
MGB/CGB Accessories
!Communication Cable
!AC Adapter
!Battery Pack Charger Set
The 6-pin serial communication subconnector and the AC adapter input connector of the
DMG hardware that preceded MGB are shaped differently than those of MGB and CGB.
Thus, two types of accessories are available — those exclusively for DMG and those
exclusively for MGB/CGB. In addition, a conversion connector is necessary for
communication between DMG and MGB/CGB.

Chapter 1: System
13
1.2 GAME Boy Block Diagram
LCD Panel
LCD Driver
8-bit
Microprocessor
Display RAM
DMG: 64 Kbit
CGB: 128 Kbit
Amp
Speaker
6-pin
Subconnector
Work RAM
DMG: 64 Kbit
CGB: 256 Kbit
Operating
Keys
Infrared
Communication
(CGB only)
Headphone
Terminal Volume
Battery External Power Source
Terminal
Power Switch
DC-DC
Converter
Mask ROM
Program
SRAM
(Backup)
Game Boy
Hardware Unit
Game Pak
Power to
System

Game Boy Programming Manual
14
1.3 Memory Configuration
In DMG and CGB,the 32 KBfrom0h to 7FFFh isavailable as program area.
000h-0FFh:Allocated as the destination addressfor RST instructions and the starting addressfor
interrupts.
100h-14Fh:Allocated as the ROM area for storing data such as the name of the game.
150h: Allocated as the starting addressof the user program.
The 8 KBfrom8000h to9FFFh isused as RAMfor the LCD display.In CGB, the amount of RAM
allocated for this purpose is 16 KB(8KB x 2), twice the amount allocated for the LCD displayin DMG,
and this RAM can be used in 8 KB units using bank switching. The 8 KBRAM areas are divided into
the following 2 areas.
1 An area for character data
2 An area for BG (background) displaydata (Character code and attribute)
The 8 KBfromA000h toBFFFh isthe areaallocated for external expansionRAM.
The 8 KBfromC000h to DFFFh isthe work RAM area.
In DMG,the 8 KBof working RAMis implemented without change. In CGB, bank switching is used to
provide 32 KBof working RAM. This 32 KBarea is divided into 8 areas of 4 KBeach.
1 The 4 KBfromC000h to CFFFh isfixed as Bank 0.
2 The 4 KBfromD000h to DFFFh can be switched between banks1 though 7.
Note: Use ofthe area fromE000htoFDFFhis prohibited.
FE00h to FFFFh isallocatedfor CPU internalRAM.
FE00h-FE9Fh: OAM-RAM (Holds displaydata for 40 objects)
FF00h-FF7Fh & FFFFh: Specifiedfor purposes such asinstructionregisters andsystem
controller flags.
FF80h-FFFEh: CanbeusedasCPU work RAMand/or stackRAM.

Chapter 1: System
15
1.4 Memory Map
Note: In DMG, there is no bank switching at 8000h-9FFFh and C000h-DFFFh.
Interrupt Address
RST Address
ROM Data
Area
User Program Area
32 KB
Bank 0
Character Data
Bank 1
Character Data
(CGB only)
BG Display Data 1 (CGB only)
Character Codes Attributes
BG Display Data 2 (CGB only)
Character Codes Attributes
External Expansion
Working RAM
8 KB
OAM (40 OBJs)
(40 x 32 bits)
Unit Working RAM
8 KB
Port/Mode Registers
Control Register
Sound Register
Working & Stack RAM
127 bytes
000h
100h
150h
8000h
9800h
9C00h
A000h
C000h
E000h
FE00h
FF00h
FFFEh
FFFFh
Bank 0 (Fixed)
Banks 1-7 (Switchable)
D000h
Lower Dot Data
Upper Dot Data
8000h
8001h
Use of area 0xE000 - 0xFDFF prohibited
Program Start Address
FF80h
FEA0h
FE00h
(OBJ 0)
FE9Fh
(OBJ 39)
Character Code
Character Code
Y0
X0
Y39
X39
Palette (DMG)
Left/Right
Up/Down
Priority
Color Palette (CGB)
Character Bank (CGB)
7 6 5 4 3 2 1 0
(DMG)
(CGB Only)

Game Boy Programming Manual
16
1.5 Feature Comparison
Item DMG CPU CGB CPU
CPU Speed
(system operating frequency) 1.05 MHz 1.05 MHz (normal mode) 2.10 MHz (double-speed mode)
Game Boy RAM
Work and Stack RAM
Work RAM
OAM
For LCD display
127 x 8 bits
8,192 bytes
40 x 28 bits
8,192 bytes
←
←←
←
32,768 bytes
40 x 32 bits
16,384 bytes
Game Pak Memory Space
ROM (without MBC)
RAM (without MBC) 32,768 bytes 8,192 bytes ←
←←
←
←
←←
←
LCD Controller
Display Capacity
Block Structure
BG, window
Object
Number of Usable Characters
BG
OBJ 8 x 8
8 x 16
Grayscale: BG, window
Grayscale: Object
Object priority
Different x coordinates
Same x coordinates
160 x 144 dots
8 x 8 dots
8 x 8 dots or 8 x 16 dots
256
256
128
4 shades, 1 palette
3 shades, 2 palettes
Object with smallest x coord .
Object with lowest OBJ number
160 x 144 x RGB dots
←
←←
←
←
←←
←
512
512
256
4 colors, 8 palettes
( DMG mode: 4 colors, 1 palette)
3 colors, 8 palettes
(DMG mode: 3 colors, 2 palettes)
Object with lowest OBJ number
(DMG mode: Object with lowest x
coord.)
←
←←
←
Timer & Divider Stages 8-bit timer x 1
16 stages x 1 ←
←←
←
←
←←
←
Serial Input/Output
Baud Rate 8 bits x 1 8 K ←
←←
←
8K/256K (16K/512K in high-speed mode
DMA Controller
Existing DMA
Horizontal blank DMA
General-purpose DMA
8000h~DFFFh→OAM
---
---
0h~DFFFh→OAM
GamePak& Work RAM→VRAM
GamePak& Work RAM→VRAM
Interrupt features
Internal Interrupts
External Interrupts 4 types (maskable) 1 type (maskable) ←
←←
←
←
←←
←
Input/Output Ports
Serial Input/Output Ports
Infrared Communication Port SIN, SCK, SOUT --- ←
←←
←
R0, R1, R2, R3
Sound Output Circuit 4 sounds ←
←←
←
Monaural (VIN) External Sound
Mixable Input
←
←←
←: Same as in column at left

Chapter 1: System
17
1.6 Register Comparison
DMG CPU CGB CPU
Use Register Address Register Address
Port/Mode
Registers P1 SB
SC
DIV
TIMA
TMA
TAC
FF00
FF01
FF02
FF04
FF05
FF06
FF07
---
---
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
KEY1
RP
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
FF4D
FF56
Bank Control
Registers --- --- VBK SVBK FF4F FF70
Interrupt
Flags IF IE
IME
FF0F
FFFF ←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
LCD Display
Registers LCDC STAT
SCY
SCX
LY
LYC
DMA
BGP
OBP0
OBP1
WY
WX
OAM
FF40
FF41
FF42
FF43
FF44
FF45
FF46
FF47
FF48
FF49
FF4A
FF4B
---
---
---
---
---
---
---
---
---
FE00~FE9F
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
HDMA1
HDMA2
HDMA3
HDMA4
HDMA5
BCPS
BCPD
OCPS
OCPD
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
←
←←
←
FF51
FF52
FF53
FF54
FF55
FF68
FF69
FF6A
FF6B
←
←←
←
Sound Registers NR x x
Waveform RAM FF10~FF26 FF30~FF3F ←
←←
←
←
←←
←←
←←
←
←
←←
←
←
←←
←: Same as in column at left

Game Boy Programming Manual
18
2. CPU
2.1 Overview of CPU Features
The CPUs of DMG and CGB are ICs customized for DMG/CGB use, and have the following features.
CPU Features
Central to the 8-bit CPU are the following features, including an I/O port and timer.
!127 x 8 bits of built-in RAM (working and stack)
!RAM for LCD Display: <DMG> 8 KB/<CGB>16 KB ( )
!Working RAM: <DMG> 8KB/<CGB> 32 KB
!Built-in 16-stage Frequency Divider
!Built-in 8-bit Timer
!4 types of Internal Interrupts (maskable)
!1 type of External Interrupt (maskable)
!Built-in DMA Controller
!Input Ports P10 ~ P13
!Output Ports P14 and P15
!Serial I/O Ports SIN, SCK, SOUT
!Infrared I/O Port <CGB only>
LCD Controller Functions
Game Boy is equipped with functions that provide control of the images displayed
on the LCD. Character data used for display is held in system RAM.
!DMG: 4 shades of gray; CGB: 32 shades of gray for each RGB color
!160 x 144-dot liquid crystal display
!8 x 8-dot composition of background and window characters
!8 x 8 or 8 x 16-dot composition of OBJ characters
!Up to 40 objects displayable in 1 screen
!Up to 10 objects displayable on 1 horizontal line
!40 x 32 bits of built-in RAM (OBJ-RAM for LCD)
!Control of 256 x 256-dot background
!Vertically and horizontally scrollable background
!Window-like functions

Chapter 1: System
19
Sound Functions
Each system is equipped with 4 types of sound synthesis circuitry.
!Sound 1: Quadrangular waveform, sweep and envelope functions
!Sound 2: Quadrangular waveform, envelope functions
!Sound 3: Arbitrary waveform, generated
!Sound 4: White noise, generated
!2 output channels (output can be allocated to a channel)
!Synthesized output with external sound input <CGB only>
Miscellaneous
!An internal monitor program is built into DMG/CGB CPUs. When power is
turned on or the Game Boy is reset, the internal monitor program first
initializes components such as the ports, then passes control to the user
program.
!Instruction cycles
<DMG> 0.954 µs (source oscillation: 4.1943 MHz)
<CGB> 0.954 µs/0.477 µs, switchable (source oscillation: 8.3886 MHz)

Game Boy Programming Manual
20
2.2 CPU Block Diagram
Game Boy (DMG/MGB) CPU
SOUT
S
FR
CPL
ST
CP
CPG
LD0
LD1
VIN
A15
A14
P10
P11
P12
P13
P14
P15
/RD
/WR
/CS
Timing
Control Data Buffer DMA
Controller
CPU Core
@@@@@@@@@
@@
ROM
RAM
127 bytes Port
P1
Divider
DIV
Timer
TIMA TMA TAC
Sound 1
NR10-NR14
Sound 2
NR20-NR23
Sound 3
NR30-NR33
Sound 4
NR40-NR42
Waveform
RAM
32 x 4
Sound
Control
NR50-NR52
OAM RAM
40 x 28 bit
LCD Display RAM Interface
SIO
SB
SC
CG
PC
H
D
B
A
SP
F
L
E
C
LCD
Drive
Signal
Buffer
LCD Controller
LCDC STAT SCY SCX LY LYC WX WY
OBP0 OBP1 BGP
Address
Buffer
A0
A1
.
.
.
.
.
.
.
.
.
/RESET D0~D7 VDD GND TEST1,2
SO1
SO2
MD0~MD7 /MCS /MWR /MRD
SIN
SCK
CK1
CK2
Ø
....
Interrupt Controller
Synthesizer
Circuit
MA0~MA12