Nintendo DMG-01 - Game Boy Console Manual page 41

TM
Game Boy CPU Manual
10. FF11 (NR 11)
Name
Contents - Sound Mode 1 register, Sound length/Wave
Wave Duty: (default: 10)
by DP
100: 31.3 ms (4/128Hz)
101: 39.1 ms (5/128Hz)
110: 46.9 ms (6/128Hz)
111: 54.7 ms (7/128Hz)
The change of frequency (NR13,NR14) at
each shift is calculated by the following
formula where X(0) is initial freq & X(t-
1) is last freq:
X(t) = X(t-1) +/- X(t-1)/2^n
- NR 11
pattern duty (R/W)
Only Bits 7-6 can be read.
Bit 7-6 - Wave Pattern Duty
Bit 5-0 - Sound length data (t1: 0-63)
00: 12.5% ( _--------_--------_-------- )
01: 25%
10: 50%
11: 75%
Sound Length = (64-t1)*(1/256) seconds
( __-------__-------__------- )
( ____-----____-----____----- )
( ______---______---______--- )
2.13.1. I/O Registers
Page 41