Nintendo DMG-01 Manual - Page 42

FF12 NR12, FF13 NR 13, FF14 NR 14

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2.13.1. I/O Registers Game BoyTM CPU Manual 11. FF12 (NR12) Name - NR 12 Contents - Sound Mode 1 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 $F. Zero being no sound. Length of 1 step = n*(1/64) seconds 12. FF13 (NR 13) Name - NR 13 Contents - Sound Mode 1 register, Frequency lo (W) Lower 8 bits of 11 bit frequency (x). Next 3 bit are in NR 14 ($FF14) 13. FF14 (NR 14) Name - NR 14 Contents - Sound Mode 1 register, Frequency hi (R/W) Only Bit 6 can be read. Bit 7 - Initial (when set, sound restarts) Bit 6 - Counter/consecutive selection Page 42 V 1.01

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2.13.1. I/O Registers
Game Boy
TM
CPU Manual
11.
FF12 (NR12)
Name
- NR 12
Contents - Sound Mode 1 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
$F. Zero being no sound.
Length of 1 step = n*(1/64) seconds
12.
FF13 (NR 13)
Name
- NR 13
Contents - Sound Mode 1 register, Frequency lo (W)
Lower 8 bits of 11 bit frequency (x).
Next 3 bit are in NR 14 ($FF14)
13.
FF14 (NR 14)
Name
- NR 14
Contents - Sound Mode 1 register, Frequency hi (R/W)
Only Bit 6 can be read.
Bit 7 - Initial (when set, sound
restarts)
Bit 6 - Counter/consecutive selection
Page 42
V 1.01