Nintendo DMG-01 Manual - Page 43

FF16 NR 21

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Game BoyTM CPU Manual 2.13.1. I/O Registers Bit 2-0 - Frequency's higher 3 bits (x) Frequency = 4194304/(32*(2048-x)) Hz = 131072/(2048-x) Hz Counter/consecutive Selection 0 = Regardless of the length data in NR11 sound can be produced consecutively. 1 = Sound is generated during the time period set by the length data in NR11. After this period the sound 1 ON flag (bit 0 of NR52) is reset. 14. FF16 (NR 21) Name - NR 21 Contents - Sound Mode 2 register, Sound Length; Wave 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) Wave Duty: (default: 10) 00: 12.5 01: 25 10: 50 11: 75 Sound Length = (64-t1)*(1/256) seconds by DP Page 43

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Game Boy
TM
CPU Manual
2.13.1. I/O Registers
Bit 2-0 - Frequency's higher 3 bits (x)
Frequency = 4194304/(32*(2048-x)) Hz
= 131072/(2048-x) Hz
Counter/consecutive Selection
0 = Regardless of the length data in
NR11 sound can be produced
consecutively.
1 = Sound is generated during the time
period set by the length data in
NR11. After this period the sound 1
ON flag (bit 0 of NR52) is reset.
14.
FF16 (NR 21)
Name
- NR 21
Contents - Sound Mode 2 register, Sound Length; Wave
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)
Wave Duty: (default: 10)
00: 12.5% ( _--------_--------_-------- )
01: 25%
( __-------__-------__------- )
10: 50%
( ____-----____-----____----- )
11: 75%
( ______---______---______--- )
Sound Length = (64-t1)*(1/256) seconds
by DP
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