Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual page 92

AGB Programming Manual
SOUND2CNT_L [d05 - 00] Sound Length
With st signifying the sound length data, the length of the output sound is
determined by the following formula.
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Address Register
SOUND2
06Ch
CNT_H
SOUND2CNT_H [d15] Initialization Flag
A setting of 1 causes Sound 2 to be restarted.
SOUND2CNT_H [d14] Sound Length
Continuous sound output with 0; with 1, sound output only for the time
specified in the sound length data of NR21.
When sound output ends, the Sound 2 ON flag of NR52 is reset.
SOUND2CNT_H [d10 - 00] Frequency Data
With fdat signifying the frequency data, the output frequency is determined
by the following formula.
Thus, the frequency range that can be specified is 64 to 131.1 KHz.
[Sound 2 Usage Note]
1. When a value is written to the envelope register, sound output
becomes unstable before the initialization flag is set. Therefore, set
initialization flag immediately after writing a value to the envelope
register.
2. For sound 2, if you change the frequency when selecting a
consecutive operation mode (Reset sound length flag of NR24),
always set 0 for data of sound length (lower 6 bits of NR21) after
setting frequency data. If 0 is not set, sound may stop prematurely.
©1999 - 2001 Nintendo of America Inc.
time ( 64 st )
NR24
Sound Length
0: Continuous
1: Counter
Initialization Flag
4194304
f
3
4 2 ( 2048
1
(sec)
256
NR23
Frequency Data
( Hz )
fdat )
92
Sound
Initial
Attributes
Value
R/W 0000h
D.C.N. AGB-06-0001-002B4