Sound2 - Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual

AGB Programming Manual
10.4 Sound 2
Sound 2 is a circuit that generates rectangular waveforms with envelope functions.
The contents of NR21, NR22, NR23, NR24 for Sound 2, conform with those of CGB.
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Address Register

SOUND2

068h
CNT_L
SOUND2CNT_L [d15 - 12] Envelope Initial-Value
Allows specification of any one of 16 levels ranging from maximum to
mute.
SOUND2CNT_L [d11] Envelope Increase/Decrease
Specifies whether volume will increase or decrease.
SOUND2CNT_L [d10 - 08] Number of Envelope Steps
Sets the length of 1 step of envelope amplification or attenuation.
With n signifying the value specified, the length of 1 step (step time) is
determined by the following formula.
When n=0, the envelope function is turned off.
SOUND2CNT_L [d07 - 06] Waveform Duty Cycle
Specifies the proportion of waveform amplitude peaks.
©1999 - 2001 Nintendo of America Inc.
NR22
No. of Envelope Steps
0-7
Envelope Increase/Decrease
0: Attenuate
1: Amplify
Envelope Initial-Value
1
steptime n
64
91
NR21
Sound Length
0-63
Waveform Duty Cycle
(sec)
Sound
Initial
Attributes
Value
R/W 0000h
D.C.N. AGB-06-0001-002B4