last update  02. Jan 08

Parts of the following text are from Jeff's FAQ document.

How does the GBA ROM cart interface work?

GBA ROMs are special chips that contain a standard ROM, address latches, and address counters all on one chip. Cart accesses can be either sequential or non-sequential. The first access to a random cart ROM location must be non-sequential. This type of access is done by putting the lower 16 bits of the ROM address on cart lines AD0-AD15 and setting /CS low to latch address lines A0-A15. Then /RD is strobed low to read 16 bits of data from that ROM location. (Data is valid on the rising edge of /RD.) The following sequential ROM location(s) can be read by again strobing /RD low. Sequential ROM access does not require doing another /CS high-to-low transitions because there are count up registers in the cart ROM chip that keep track of the next ROM location to read. Address increment occurs on the low-to-high edge of all /RD. In theory, you can read an entire GBA ROM with just one non-sequential read (address 0) and all of the other reads as sequential so address counters must be used on most address lines to exactly emulate a GBA ROM. However, you only need to use address latch / counters on A0-A15 in order to satisfy the GBA since A16-A23 are always accurate. For more details, take a look    here :-)

What is the largest size ROM supported by GBA?

The GBA cart interface has 24 address lines. Also there are 16 data lines. 24 address lines = 2^24 = 16.7 million locations which means 16M x 16bit or 32M x 8bit. Which is a total of 32MBytes or 256Mbits of memory space. To put more memory than this in a cart would require some form of bankswitching.

Pinning of the GBA connector

and my sample for connecting RAM or Flash ROM at 0x0E000000 is here.  For the flash ROM at 0x08000000 you will need address latch / counters on AD0 - AD15. See the schematic below for more details.

What type of backup methods are currently used in GBA carts?

SRAM (256KBit or 512Kbit) - Battery backed up static RAM. It can be up to 64K bytes but it's usually 32K bytes in size. It is located in the memory map from 0xe000000 to 0xe00ffff. (Examples of games that use 32K RAM backup: FZero, etc.). Newer games are using 64K bytes.

Flash ROM (512KBit or 1Mbit) - This is memory which can be 64K bytes or 128K bytes with bank switching. It is located in the memory map from 0xe000000 to 0xe00ffff. Reading Flash ROM is the same as reading SRAM; however, writing to Flash ROM is a different process due to the fact that Flash chips often have different modes of operation. Consult Sanyo & Atmel flash data sheets for more info. 

This type of backup is emulated in nearly all available cartridges. Cart designers only have to implement the identify, the erase (in case of Sanyo based design) and the write command. Not a big problem inside an EPLD design :-) and it's enough to implement only one chip :-).

Here are the 512Kbit (64Kbyte) and 1Mbit (128Kbyte) chip types used inside GBA cartridges:

Some of the manufacturers guarantee a minimum of 10,000 rewrites per 1 sector so these devices have a limited life compared to SRAM. (Examples of games that use 64K Flash ROM backup: GT:Grand Touring Car Championship, Chu Chu Rocket, etc.) The Pokemon Ruby cartridge will use a 1Mbit flash chip.

EEPROM (4KBit or 64KBit) - This uses the /CS, A23, and D0 of the cart bus and is a serial connection. It usually is found in 4kbit or 64kbit size, but because of it's serial configuration, it could theoretically be any size. The maximum useable ROM size is 128MBits when using this device. Some of the manufacturers guarantee a minimum of 100,000 rewrites per address so these devices have a limited life compared to SRAM. (Examples of games that use EEPROM backup: Mario Advance, Final Fight, Hot Potato).

The older Visoly (ASIC based) cartridges can only emulate 4K EEPROM's. Newer games with 64K EEPROM's will have problems with backup save. In this case you should use the patch program.

DACS (1MBit or 8MBit) - the Debugging And Communication System with 1MBit or 8MBit custom flash memory with security and patch functions is not used at the moment. It is located in the upper ROM area and will reduce the maximum ROM size to 255MBit or 248MBit.

  Here is the first home-made flash cart :-)

It's a 8MB flash cart from Timmy Brolin without RAM, but you will see all GBA details. Homepage is here.

Here is my design of a GBA flash cartridge with single Flash, SRAM and EPM3064 :-)

  Here is a first example of a home-made cart reader and also an USB programmer. 

Take a look on the developers page.

 great GBA hardware !!!

  commercial programming hardware

DadyCool's homepage for a great cartridge programming software (LittleWriter) including EEPROM and speed patching is here.

  Information about commercial GBA cartridges:

1 only 256MB version     2  with Littlewriter software    3 with GBA FLinker software by Jeff Frohwein

Be sure to check out the recent EDN article Gaming as Serious Business, which describes both potential and actual applications of the Game Boy as a microcontroller. 

Snicker about playing games at work, but the low cost, appropriate features, and availability of Gameboy resources might change your mind about using it as a nongaming, handheld terminal.
By Robert Cravotta, Technical Editor -- EDN, 2/7/2002     here is a short link :-)

Here is another great article ( Gameboy Advance for nongaming applications) from Aarul Jain and Dhananjay V. Gadre published in Dr.Dobb's Journal, May 2004.

Flash cartridge summary:

  Information about GBA Multiboot hard- and software:

The multiboot hardware is a cable that connects to either a PC parallel or serial port and to the link port on the GameBoy Advance itself. It allows you to test small GBA programs (256K bytes or less), that you have created yourself, on real GBA hardware. It takes advantage of the fact that each GameBoy Advance has a built-in boot algorithm for loading code over the link port into external WRAM (256k bytes) and then executing this code. (External WRAM is actually inside of the GBA itself.) As such, no cart is required to be installed in the GBA to use this cable.

Description of the GBA link-port

Here is a great schematic from Dark Fader for the GBA link port.   This port is no USB interface!

These tools here allow you to upload data, images to the GBA and debug programs by using a simple UART (normal serial port) cable. Jeff's faq is also helpfull :-)

This cable does not let you upload a program to the GBA using multi-boot protocol !

Andrew May also described the link port. Take a look here.