Sound 4 Mode Registers - Nintendo GAME BOY Programming Manual

♦ ♦ ♦ ♦ Sound 3 Usage Notes
• • • • The initialization flag should not be set when the frequency is changed during Sound
3 output.
• • • • Setting the initialization flag during Sound 3 operation (Sound 3 ON flag = 1) may
destroy the contents of waveform RAM.
• • • • Setting the initialization flags for Sound 1, Sound 2, or Sound 4 does not cause a problem.
♦ ♦ ♦ ♦ Waveform RAM Composition
Waveform RAM consists of waveform patterns of 4 bits x 32 steps.
Address
FF30
FF31
FF32
FF3F
Example: Triangular Wave
Data
FH
OH

2.4 Sound 4 Mode Registers

Sound 4 is a white-noise generating circuit. It can output sound while switching the number of steps of the
polynomial counter for random number generation and changing the frequency dividing ratio and
envelope data by registers NR41, NR42, NR43, and NR44.
Name Address Bit 7
NR41 FF20
D7 D6 D5
Step 0
Step 2
Step 4
Step 30
OH
6 5 4 3 2 1
D4 D3
FF30H -- 01H, 23H, 45H, 67H
89H, ABH, CDH, EFH,
EDH, CBH, A9H, 87H
65H, 43H, 21H, 00H
1FH
0
R/W
Sound Length,t1(0 to 63)
87
Chapter 3: Sound Functions
D2 D1 D0
Step 1
Step 3
Step 5
Step 31