Nintendo DMG-01 - Game Boy Console Manual page 48

2.13.1. I/O Registers
25. FF22 (NR 43)
Name
Contents - Sound Mode 4 register, polynomial
Page 48
Bit 2-0 - Number of envelope sweep
Initial volume of envelope is from 0 to
$F. Zero being no sound.
Length of 1 step = n*(1/64) seconds
- NR 43
counter (R/W)
Bit 7-4 - Selection of the shift clock
Bit 3 - Selection of the polynomial
Bit 2-0 - Selection of the dividing ratio
Selection of the polynomial counter step:
0: 15 steps
1: 7 steps
(n: 0-7) (If zero, stop
envelope operation.)
frequency of the polynomial
counter
counter's step
of frequencies:
000: f * 1/2^3 * 2
001: f * 1/2^3 * 1
010: f * 1/2^3 * 1/2
011: f * 1/2^3 * 1/3
100: f * 1/2^3 * 1/4
101: f * 1/2^3 * 1/5
110: f * 1/2^3 * 1/6
111: f * 1/2^3 * 1/7
f = 4.194304 Mhz
TM
Game Boy CPU Manual
V 1.01