The Sidney Affair: Routine at FBC7

FBC7: Sound: Noise

Makes a short noise on the speaker by toggling bit 4 of port FE for 0080 pulses. Called by BASIC as "noi" (FBC7).
Sound_Noise	FBC7	DI	Disable interrupts.
	FBC8	LD BC,$0080
	FBCB	LD A,($5C48)
	FBCE	RRCA
	FBCF	RRCA
	FBD0	RRCA
	FBD1	EX AF,AF'
	FBD2	LD H,$00
Sound_Noise_0	FBD4	EX AF,AF'
	FBD5	OUT ($FE),A
	FBD7	XOR $10
	FBD9	EX AF,AF'
	FBDA	LD L,$00
	FBDC	LD D,L
	FBDD	LD E,H
	FBDE	AND A
	FBDF	SBC HL,DE
	FBE1	SBC HL,DE
	FBE3	LD DE,$00FE
	FBE6	ADD HL,DE
	FBE7	LD A,L
	FBE8	SUB H
	FBE9	JR C,Sound_Noise_1
	FBEB	DEC A
Sound_Noise_1	FBEC	LD H,A
Sound_Noise_2	FBED	DEC A
	FBEE	JR NZ,Sound_Noise_2
	FBF0	DEC BC
	FBF1	LD A,B
	FBF2	OR C
	FBF3	JR NZ,Sound_Noise_0
	FBF5	RET