Nintendo GAME BOY Programming Manual page 82

Game Boy Programming Manual
Example: When NR10 = 79h and the default frequency = 400h, the sweep waveform appears as follows.
7.8ms
Note: When the sweep function is not used, the increase/decrease flag should be set
to 1 (subtraction mode).
Name Address Bit 7
NR11 FF11
Sound length = (64 - t1) x (1/256) sec
Waveform Duty Cycles
Name Address Bit 7
NR12 FF12
Length of Envelope Steps:
Sets the length of each step of envelope amplification or attenuation.
Length of 1 step = N x (1/64) sec
When N = 0, the envelope function is stopped.
Default Envelope Value (0000 to 1111B):
16 step levels can be specified using the 4-bit D/A circuit.
Maximum is 1111B, and 0000 is the mute setting.
11.7ms
54.7ms
6 5 4 3 2 1
00 : 12.5%
01 : 25%
10 : 50%
11 : 75%
6 5 4 3 2 1
54.7ms
0
R/W(Only the shaded portion
( ) can be read.)
Sound Length, t1(0 to 63)
Waveform Duty Cycle
0
R/W
Length of Envelope Steps n(n=0 to 7)
Envelope Up/Down
0: Attenuate(decrease)
1: Amplify(increase)
Default Envelope Value
82
13.6ms
54.7ms