Power Up Sequence - Revision history

Nitro2k01 at 02:42, 5 April 2020

2020-04-05T02:42:47Z

T4g1: Labl error corrected

2018-05-25T17:39:28Z

Labl error corrected

Xzakox at 13:02, 28 June 2009

2009-06-28T13:02:58Z

Xzakox: New page: 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 ...

2009-06-28T11:07:28Z

New page: 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 ...

New page

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. If all locations compare the same, then 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. If it is a zero, then the internal ROM is disabled and cartridge program execution begins at location $100 with the following register values:

AF=$01B0
BC=$0013
DE=$00D8
HL=$014D
Stack Pointer=$FFFE
[$FF05] = $00 ; TIMA
[$FF06] = $00 ; TMA
[$FF07] = $00 ; TAC
[$FF10] = $80 ; NR10
[$FF11] = $BF ; NR11
[$FF12] = $F3 ; NR12
[$FF14] = $BF ; NR14
[$FF16] = $3F ; NR21
[$FF17] = $00 ; NR22
[$FF19] = $BF ; NR24
[$FF1A] = $7F ; NR30
[$FF1B] = $FF ; NR31
[$FF1C] = $9F ; NR32
[$FF1E] = $BF ; NR33
[$FF20] = $FF ; NR41
[$FF21] = $00 ; NR42
[$FF22] = $00 ; NR43
[$FF23] = $BF ; NR30
[$FF24] = $77 ; NR50
[$FF25] = $F3 ; NR51
[$FF26] = $F1-GB, $F0-SGB ; NR52
[$FF40] = $91 ; LCDC
[$FF42] = $00 ; SCY
[$FF43] = $00 ; SCX
[$FF45] = $00 ; LYC
[$FF47] = $FC ; BGP
[$FF48] = $FF ; OBP0
[$FF49] = $FF ; OBP1
[$FF4A] = $00 ; WY
[$FF4B] = $00 ; WX
[$FFFF] = $00 ; IE

It is not a good idea to assume the above values will always exist. A later version GameBoy could contain different values than these at reset. Always set these registers on reset rather than assume they are as above.

Please note that GameBoy internal RAM on power up contains random data. All of the GameBoy emulators tend to set all RAM to value $00 on entry.

Cart RAM the first time it is accessed on a real GameBoy contains random data. It will only contain known data if the GameBoy code initializes it to some value.

← Older revision		Revision as of 02:42, 5 April 2020
Line 1:		Line 1:
−	{{Pandocs\|~~powerupsequence~~}}	+	{{Pandocs\|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. If all locations compare the same, then 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. If it is a zero, then the internal ROM is disabled and cartridge program execution begins at location $100 with the following register values:		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. If all locations compare the same, then 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. If it is a zero, then the internal ROM is disabled and cartridge program execution begins at location $100 with the following register values:

← Older revision		Revision as of 13:02, 28 June 2009
Line 1:		Line 1:
		+	{{Pandocs\|powerupsequence}}
	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. If all locations compare the same, then 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. If it is a zero, then the internal ROM is disabled and cartridge program execution begins at location $100 with the following register values:		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. If all locations compare the same, then 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. If it is a zero, then the internal ROM is disabled and cartridge program execution begins at location $100 with the following register values:

@@ Line 24: / Line 24: @@
     [$FF21] = $00   ; NR42
     [$FF22] = $00   ; NR43
-    [$FF23] = $BF   ; NR30
+    [$FF23] = $BF   ; NR44
     [$FF24] = $77   ; NR50
     [$FF25] = $F3   ; NR51