Nintendo GAME BOY Programming Manual page 273

2. SOUND REGISTER SUMMARY
All values shown in the following table apply to normal mode. The values for double-speed mode should be
calculated by doubling the system clock frequency.
Register Address
NR10 FF10
FF11
NR11
Duty
cycle/sound
length
S
NR12 FF12
O
U
Envelope
N
D
NR13 FF13
1
Lower-order
frequency
data
NR14 FF14
Higher-order
frequency
data/
other
D7 D6 D5
Sweep time: 010:15.6ms
101:39.1ms
000:OFF 011:23.4ms
110:46.9ms
001:7.8ms 100:31.3ms
111:54.7ms
Sound length data t1 : 0 - 63
Waveform duty cycle
Sound length = (64-t1) * (1/256) sec
00: 12.5% 10: 50%
01: 25% 11: 75%
Initial envelope value: 0x00 – 0x0F
Mute when 0x00
Maximum when 0x0F
Lower-order 8 bits of frequency data
Restart Length
when selection
initialize 0:
flag Consecutive
set to 1 1: NR11
Appendix 2. Register and Instruction Set Summaries
D4 D3 D2
Sweep
increase Number of sweep shifts: 0 - 7
/decrease
0: + f hi
1: - f low
Envelope Number of envelope steps N = 0 - 7
U/D Length of 1 step = N*(1/64) sec
0: Attenuate Envelope function stopped when N=0
1: Amplify
Higher order 3 bits of frequency
data
With x =11-bit frequency data,
f = 4194304 / (4*2
273
D1 D0 Comment
R/W
f =128Hz
128
R/W
R/W
Initial value of
00 sets to OFF
when in DOWN
mode
W
R/W
f = 64Hz -
131KHz
3
(2048-x)) Hz