Nintendo GAME BOY Programming Manual page 80

Game Boy Programming Manual
♦ ♦ ♦ ♦ OFF Mode
Stops operation of the frequency counter and D/A converter and halts sound output.
♦ ♦ ♦ ♦ Sounds 1, 2, and 4:
-When the default level is set to 0000 with the envelope in DOWN mode
(initialization not required)
♦ ♦ ♦ ♦ Sound 3:
-When the Sound OFF flag (bit 7 of NR30) is set to 0.
Setting the Sound OFF flag to 1 cancels OFF mode.
Sound 3 is started by re-initialization.
♦ ♦ ♦ ♦ All Sounds OFF mode
-Setting the All Sounds ON/OFF flag (bit 7 of NR52) to 0 resets all of the
mode registers (for sounds 1, 2, 3, and 4) and halts sound output. Setting
the All Sounds ON/OFF flag to 1 cancels All Sounds OFF mode.
Note: The sound mode registers should always be set after All Sound OFF mode is
cancelled. The sound mode registers cannot be set in All Sound OFF mode.
♦ ♦ ♦ ♦ Sound Usage Notes
Use one of the following methods to halt sounds 1, 2, or 4.
1) Use NR51.
2) Set NR12, NR22, and NR42 to 0x08.
3) Set NR14, NR24, and NR44 to 0x80.
Switch to OFF mode during the scene you stop the BGM. Unless you switch to OFF mode, a faint
whining noise can be heard due to the sound circuit structure.
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