Routines
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68B1: Play square wave sound
Used by the routines at 6825, 683E, LevelStartJingle and 6888.
Input
D Duration of wave
PlaySquareWave 68B1 LD A,$10 Play square wave sound.
68B3 OUT ($FE),A
68B5 LD B,D
PlaySquareWave_Loop 68B6 DJNZ PlaySquareWave_Loop
68B8 XOR A Play "silence".
68B9 OUT ($FE),A
68BB LD B,D
Silence_Loop 68BC DJNZ Silence_Loop
68BE RET Return.
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