Sound4 - Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual

AGB Programming Manual
10.6 Sound 4
Sound 4 is a circuit that generates white noise with the envelope function.
The contents of NR41, NR42, NR43, and NR44 for Sound 4 conform with those of
CGB.
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Address Register

SOUND4

078h
CNT_L
SOUND4CNT_L [d15 - 12] Envelope Initial-Value
Allows specification of any of 16 levels ranging from maximum to mute.
SOUND4CNT_L [d11] Envelope Increase/Decrease
Specifies whether to increase or decrease the volume.
SOUND4CNT_L [d10 - 08] Number of Envelope Steps
Sets the length of each step of envelope amplification or attenuation.
With n the specified value, the length of 1 step (steptime) is determined by
the following formula.
When n = 0, the envelope function is turned off.
SOUND4CNT_L [d05 - 00] Sound Length
With st signifying the sound length, the length of the output sound is
determined by the following formula.
©1999 - 2001 Nintendo of America Inc.
NR42
No. of Envelope Steps
0-7
Envelope Increase/Decrease
0: Attenuate
1: Amplify
Envelope Initial-Value
1
steptime n
64
time ( 64 st )
97
NR41
Sound Length
0-63
(sec)
1
(sec)
256
Sound
Initial
Attributes
Value
R/W 0000h
D.C.N. AGB-06-0001-002B4