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
   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.