Nintendo DMG-01 Manual - Page 17

Special modi

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Game BoyTM CPU Manual 2.7. Special modi 2.7. Special modi 2.7.1. Power Up Sequence When the GameBoy is powered up, a 256 byte program starting at memory location 0 is executed. This program is located in a ROM inside the GameBoy. The first thing the program does is read the cartridge locations from $104 to $133 and place this graphic of a Nintendo logo on the screen at the top. This image is then scrolled until it is in the middle of the screen. Two musical notes are then played on the internal speaker. Again, the cartridge locations $104 to $133 are read but this time they are compared with a table in the internal rom. If any byte fails to compare, then the GameBoy stops comparing bytes and simply halts all operations. GB & GB Pocket: Next, the GameBoy starts adding all of the bytes in the cartridge from $134 to $14d. A value of 25 decimal is added to this total. If the least significant byte of the result is a not a zero, then the GameBoy will stop doing anything. Super GB: Even though the GB & GBP check the memory locations from $134 to $14d, the SGB doesn't. If the above checks pass then the internal ROM is disabled and cartridge program execution begins at location $100 with the following register values: AF=$01-GB/SGB, $FF-GBP, $11-GBC F =$B0 by DP Page 17

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Game Boy
TM
CPU Manual
2.7. Special modi
2.7.
Special modi
2.7.1.
Power Up Sequence
When the GameBoy is powered up, a 256 byte program
starting at memory location 0 is executed. This
program is located in a ROM inside the GameBoy. The
first thing the program does is read the cartridge
locations from $104 to $133 and place this graphic of
a Nintendo logo on the screen at the top. This image
is then scrolled until it is in the middle of the
screen. Two musical notes are then played on the
internal speaker. Again, the cartridge locations $104
to $133 are read but this time they are compared with
a table in the internal rom.
If any byte fails to compare, then the GameBoy stops
comparing bytes and simply halts all operations.
GB & GB Pocket:
Next, the GameBoy starts adding all of the bytes
in the cartridge from $134 to $14d. A value of 25
decimal is added to this total. If the least
significant byte of the result is a not a zero,
then the GameBoy will stop doing anything.
Super GB:
Even though the GB & GBP check the memory
locations from $134 to $14d, the SGB doesn't.
If the above checks pass then the internal ROM is
disabled and cartridge program execution begins at
location $100 with the following register values:
AF=$01-GB/SGB, $FF-GBP, $11-GBC
F =$B0
by DP
Page 17