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https://github.com/tophercantrell/retro-gameboy

Hardware and Software Development on the GBC
https://github.com/tophercantrell/retro-gameboy

cartridge gameboy-color

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Hardware and Software Development on the GBC

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README 

        
# Nintendo Game Boy



Gameboy/GameboyColor homebrew development is nothing new. There are lots of tutorials on GB/GBC 

hacking (see the links below). This repo is a journal of my experience and any code I produced 

along the way. 



Journal here: [Journal](journal.md)



[Building a Development Cartridge](CARTRIDGE.md)



## Links



Nice, concise listing of registers and opcode changes:

[Tech info](http://fms.komkon.org/GameBoy/Tech/Software.html)



[Wikipedia](https://en.wikipedia.org/wiki/Game_Boy_Color)



[http://www.loirak.com/gameboy/gbprog.php](http://www.loirak.com/gameboy/gbprog.php)



[http://gbdev.gg8.se/wiki/articles/Main_Page](http://gbdev.gg8.se/wiki/articles/Main_Page)



[Javascript Emulator and Tutorial](https://imrannazar.com/series/gameboy-emulation-in-javascript)



## Hardware Overview



The Gameboy hardware line is wonderfully backwards compatible. The Gameboy Advanced (GBA) has 

two cartridge slots: one for GBA games and one for old Gameboy/GameboyColor games you may own.



The Gameboy (GB) has a special Z80 processor with a few opcode differences. There is a boot ROM in the console that 

draws a splash screen and transfers control to any cartridge plugged in.



The GameboyColor (GBC) is the GB with additional hardware. The processor and memory layout is the same. GB games play fine 

on the GBC. The GB uses 4 AA batteries (6V). The GBC uses 2 AA batteries (3V) but has a power boot to crank 3V up to 5 to 

run the console and cartridge.



The cartridge connector is one-sided, 32 pins. The signals are power, ground, clock, read, write, chip-select, reset, audio, 16 address lines, and 8 data lines. 



![](art/cartPinout.png)



The Z80's address space is split nicely in half. The lower 32K (A15=0) is ROM space in the cartridge. The upper

32K (A15=1) is for hardware registers, system RAM, and an additional 8K RAM area in the cartridge.



Most cartridges include extra RAM (often battery-backed) and ROMs much larger than 32K. Nintendo used a line of

bank-switching chips like MBC5 in each cartridge to select banks of RAM and ROM in the cartridge. I'll discuss

the MBC more in the programming section below. The chip generates the upper address lines (A14 and up) from

internal latches you twiddle by writing to the ROM address space.



# Game Boy Advanced Development



I wrote code for the Game Boy Advanced years ago. See [Circuit Cellar Magazine, February 2006](http://www.cc-webshop.com/Circuit-Cellar-Issue-187-February-2006-PDF-FI-2006-187.htm). Back 

then I had a nice XPort cartridge to link my computer to the GBA. There was no hardware work

involved -- just C++ and learning the hardware registers on the GBA.