Nintendo DMG-01 Manual - Page 44

FF17 NR 22, FF18 NR 23, FF19 NR 24

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2.13.1. I/O Registers Game BoyTM CPU Manual 15. FF17 (NR 22) Name - NR 22 Contents - Sound Mode 2 register, envelope (R/W) Bit 7-4 - Initial volume of envelope Bit 3 - Envelope UP/DOWN 0: Attenuate 1: Amplify Bit 2-0 - Number of envelope sweep (n: 0-7) (If zero, stop envelope operation.) Initial volume of envelope is from 0 to $F. Zero being no sound. Length of 1 step = n*(1/64) seconds 16. FF18 (NR 23) Name - NR 23 Contents - Sound Mode 2 register, frequency lo data (W) Frequency's lower 8 bits of 11 bit data (x). Next 3 bits are in NR 14 ($FF19). 17. FF19 (NR 24) Name - NR 24 Contents - Sound Mode 2 register, frequency hi data (R/W) Only bit 6 can be read. Bit 7 - Initial (when set, sound Page 44 V 1.01

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2.13.1. I/O Registers
Game Boy
TM
CPU Manual
15.
FF17 (NR 22)
Name
- NR 22
Contents - Sound Mode 2 register, envelope (R/W)
Bit 7-4 - Initial volume of envelope
Bit 3 -
Envelope UP/DOWN
0: Attenuate
1: Amplify
Bit 2-0 - Number of envelope sweep
(n: 0-7) (If zero, stop
envelope operation.)
Initial volume of envelope is from 0 to
$F. Zero being no sound.
Length of 1 step = n*(1/64) seconds
16.
FF18 (NR 23)
Name
- NR 23
Contents - Sound Mode 2 register, frequency
lo data (W)
Frequency's lower 8 bits of 11 bit data
(x). Next 3 bits are in NR 14 ($FF19).
17.
FF19 (NR 24)
Name
- NR 24
Contents - Sound Mode 2 register, frequency
hi data (R/W)
Only bit 6 can be read.
Bit 7 - Initial (when set, sound
Page 44
V 1.01