Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual page 90

AGB Programming Manual
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Address Register
SOUND1
064h
CNT_X
SOUND1CNT_X [d15] Initialization Flag
A setting of 1 causes Sound 1 to restart.
When the sweep function is used, set the initialization flag again after an
interval of 8 clocks or more.
SOUND1CNT_X [d14] Sound Length Flag
When 0, sound is continuously output.
When 1, sound is output for only the length of time specified for the sound
length in NR11.
When sound output ends, the Sound 1 ON flag of NR52 is reset.
SOUND1CNT_X [d10 - 00] Frequency Data
With fdat signifying the frequency, the output frequency (f) is determined by
the following formula.
Thus, the specifiable range of frequencies is 64 to 131.1 KHz.
[Sound 1 Usage Notes]
1. When the sweep function is not used, the sweep time should be set to 0 and the
sweep increase/decrease flag should be set to 1.
2. If sweep increase/decrease flag of NR10 is set to 0, the number of sweep shifts
set to a non-zero value, and sweep OFF mode is set, sound production may be
stopped.
3. 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.
4. For sound 1, if you change the frequency when selecting a consecutive operation
mode (sound length flag of NR14 is 0), always set 0 for the data of sound length
(lower 6 bits of NR11) after setting the frequency data. If 0 is not set, sound may
stop prematurely.
5. If the Sound 1 initialization flag is set when the sweep function is used, always set
the initialization flag again after an interval of 8 clocks or more. Unless the
initialization flag is set twice with an interval of 8 clocks or more, the sound may
not be heard.
©1999 - 2001 Nintendo of America Inc.
NR14
Sound Length Flag
0: Continuous
1: Counter
Initializaton Flag
4194304
f
3
4 2 (
NR13
Frequency Data
Hz
2048 fdat )
90
Sound
Initial
Attributes
Value
R/W 0000h
D.C.N. AGB-06-0001-002B4