Nintendo 1504166 - Game Boy Advance SP Edition Console Programming Manual page 88

AGB Programming Manual
SOUND1CNT_L [d02 - 00] Number of Sweep Shifts
Specifies the number of sweeps.
The frequency data with a single shift are determined according to the
following formula, with f
frequency before the shift.
If the addition according to this formula produces a value consisting of
more than 11 bits, sound output is stopped and the Sound 1 ON flag (bit 0)
of NR52 is reset.
With subtraction, if the subtrahend is less than 0, the pre-subtraction value
is used. However, if the specified setting is 0, shifting does not occur and
the frequency is unchanged.
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
Address Register
SOUND1
062h
CNT_H
SOUND1CNT_H [d15 - 12] Envelope Initial-Value
Allows specification of any of 16 levels ranging from maximum to mute.
SOUND1CNT_H [d11] Envelope Increase/Decrease
Specifies whether to increase or decrease the volume.
©1999 - 2001 Nintendo of America Inc.
signifying the frequency after a shift and f
(t)
f
( t ) 1
f f
( t ) ( t ) 1
n
2
f Initial frequency
( ) 0
NR12
No. of Envelope Steps
0-7
Envelope Increase/Decrease
0: Attenuate
1: Amplify
Envelope initial value
88
data
Attributes
NR11
R/W
Sound Length
0-63
Waveform duty cycle
Sound
the
(t-1)
Initial Value
0000h
D.C.N. AGB-06-0001-002B4