Nintendo GAME BOY Programming Manual page 275

Register Address
NR41 FF20
Sound
length data
NR42 FF21
S
O
Envelope
U
N
D
NR43 FF22
4
Polynomial
counter
NR44 FF23
Initialize/length
NR50 FF24
SO1 / SO2
level
C
O
NR51 FF25
N
T
Distribution
R
to
O
SO1/SO2
L
NR52 FF26
Sound-end
flag
D7 D6 D5
Sound length data t1 : 0 - 63
Sound length = (64-t1) * (1/256) sec
Initial envelope value 0x00 –
0x0F
Mute when 0x00
Max when 0x0F
Polynomial counter clock
frequency selection
Prohibited codes
13
0000: f * 1/2 1100: f * 1/2
b b
2 14
0001: f * 1/2 1101: f * 1/2
b b
Restart Length
when selection
initialize 0:
flag set Consecutive
to 1 1: NR41
VIN SO2 output level control
input 000 (min) – 111 (max)
0:SO2
OFF
1:SO2
output
Sound Sound Sound
4 to 3 to 2 to
SO2 SO2 SO2
All
sounds
0:
Stop
1:
Play
Appendix 2. Register and Instruction Set Summaries
D4 D3 D2
Envelope Number of envelope steps N = 0-7
U/D Length of 1 step = N*(1/64) sec
0: Envelope function stops when N=0
Attenuate
1: Amplify
Step no. Selection of frequency dividing
selection ratio f
0: 15 000: f*1/2
1110 steps 001: f*1/2
1111 1: 7 f*1/2
steps
VIN input SO1 output level control
0:SO1 000 (min) – 111 (max)
OFF
1:SO1
output
Sound Sound Sound
1 to 4 to 3 to
SO2 SO1 SO1
Sound Sound
4 3
ON flag ON flag
275
D1 D0
b
3 3
*2 110: f*1/2 *1/6
3
*1/1 to 000:
3
*1/7
Sound Soun
2 to d 1 to
SO1 SO1
Sound 2 Sound
ON flag 1
ON flag
Comment
R/W
R/W
Initial value of
00 sets to OFF
when in DOWN
mode
W
f =
4.194304MHz
R/W
R/W
R/W
0: No output
1: Output
R/W