Spellbound (48k): Routine at 38075

38075: Set parameters for and play upward scale sound

The value of A (set to zero at the start of this routine, or set to 1 before jumps from other routines into 38080) is a delay constant that determines the speed at which the sound is played.

Used by the routines at 30222, 30439, 30602, 30880, 31370, 31636, 32035, 32194, 32258, 32390, 32655, 33312, 33593, 33663, 38749 and 54996.

Input
A	(Entry at 38080 only) Delay constant

38075

XOR A

Set A to 0

38076

LD B,13

Set B to 13 (DEC C)

38078

LD H,A

Set HL to 0...

38079

LD L,A

...

This entry point is used by the routines at 38108 and 38116.

38080

LD (38094),A

Modify instruction at 38093 with value of delay constant

38083

LD A,B

Load B into A

38084

LD (38102),A

Set instruction at 38102

38087

LD (38103),HL

Set instructions at 38103 and 38104

38090

CALL 38212

Load A with current border colour

The operand of the instruction at 38093 represents the value of the delay constant. This is modified by the instruction at 38080.

38093

LD C,0

Load C with delay constant

38095

OUT (254),A

Set border colour, and reset ear/speaker

38097

XOR 16

Invert ear/speaker bit of A

38099

LD B,C

Load C (delay constant) into B...

38100

DJNZ 38100

...and delay

The instructions at 38102 - 38104 represent the manipulation of the delay constant between iterations of this routine. These instructions may decrease C by one, increase C by three or do nothing. These instructions are modified by the instructions at 38084 and 38087.

38102

DEC C

Decrease / increase delay constant for next pass, increasing / decreasing pitch of tone respectively

38103

NOP

Do nothing, or increase delay constant

38104

NOP

Do nothing, or increase delay constant

38105

JR NZ,38095

If delay constant is not zero, then loop back to continue playing tone

38107

RET

Return