Nintendo DMG-01 Manual - Page 45

FF1A NR 30, FF1B NR 31

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Game BoyTM CPU Manual 2.13.1. I/O Registers restarts) Bit 6 - Counter/consecutive selection 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 NR21 sound can be produced consecutively. 1 = Sound is generated during the time period set by the length data in NR21. After this period the sound 2 ON flag (bit 1 of NR52) is reset. 18. FF1A (NR 30) Name - NR 30 Contents - Sound Mode 3 register, Sound on/off (R/W) Only bit 7 can be read Bit 7 - Sound OFF 0: Sound 3 output stop 1: Sound 3 output OK 19. FF1B (NR 31) Name - NR 31 Contents - Sound Mode 3 register, sound length (R/W) Bit 7-0 - Sound length (t1: 0 - 255) Sound Length = (256-t1)*(1/2) seconds by DP Page 45

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Game Boy
TM
CPU Manual
2.13.1. I/O Registers
restarts)
Bit 6 - Counter/consecutive selection
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
NR21 sound can be produced
consecutively.
1 = Sound is generated during the time
period set by the length data in
NR21. After this period the sound 2
ON flag (bit 1 of NR52) is reset.
18.
FF1A (NR 30)
Name
- NR 30
Contents - Sound Mode 3 register, Sound on/off (R/W)
Only bit 7 can be read
Bit 7 - Sound OFF
0: Sound 3 output stop
1: Sound 3 output OK
19.
FF1B (NR 31)
Name
- NR 31
Contents - Sound Mode 3 register, sound length (R/W)
Bit 7-0 - Sound length (t1: 0 - 255)
Sound Length = (256-t1)*(1/2) seconds
by DP
Page 45