Sound - Nintendo DMG-01 - Game Boy Console Manual

2.9. Sound

2.9. Sound
There are two sound channels connected to the output
terminals SO1 and SO2. There is also a input terminal
Vin connected to the cartridge. It can be routed to
either of both output terminals. GameBoy circuitry
allows producing sound in four different ways:
Quadrangular wave patterns with sweep and envelope
functions. Quadrangular wave patterns with envelope
functions. Voluntary wave patterns from wave RAM.
White noise with an envelope function.
These four sounds can be controlled independantly and
then mixed separately for each of the output
terminals.
Sound registers may be set at all times while
producing sound.
When setting the initial value of the envelope and
restarting the length counter, set the initial flag to
1 and initialize the data.
Under the following situations the Sound ON flag is
reset and the sound output stops:
1. When the sound output is stopped by the length
counter.
2. When overflow occurs at the addition mode while
sweep is operating at sound 1.
When the Sound OFF flag for sound 3 (bit 7 of NR30)
is set at 0, the cancellation of the OFF mode must be
done by setting the sound OFF flag to 1. By
initializing sound 3, it starts it's function.
Page 28
TM
Game Boy CPU Manual
V 1.01