Routines
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38562: Play the theme tune (Moonlight Sonata)
Used by the routine at 34762. For each of the 99 bytes in the tune data table at 34299, this routine produces two notes, each lasting approximately 0.15s; the second note is played at half the frequency of the first. Returns with the zero flag reset if ENTER, 0 or the fire button is pressed while the tune is being played.
Input
HL 34299
38562 LD A,(HL) Pick up the next byte of tune data from the table at 34299
38563 CP 255 Has the tune finished?
38565 RET Z Return (with the zero flag set) if so
38566 LD BC,100 B=0 (short note duration counter), C=100 (short note counter)
38569 XOR A A=0 (border colour and speaker state)
38570 LD E,(HL) Save the byte of tune data in E for retrieval during the short note loop
38571 LD D,E Initialise D (pitch delay counter)
38572 OUT (254),A Produce a short note (approximately 0.003s) whose pitch is determined by the value in E
38574 DEC D
38575 JR NZ,38580
38577 LD D,E
38578 XOR 24
38580 DJNZ 38572
38582 EX AF,AF' Save A briefly
38583 LD A,C Is the short note counter in C (which starts off at 100) down to 50 yet?
38584 CP 50
38586 JR NZ,38590 Jump if not
38588 RL E Otherwise double the value in E (which halves the note frequency)
38590 EX AF,AF' Restore the value of A
38591 DEC C Decrement the short note counter in C
38592 JR NZ,38572 Jump back unless we've finished playing 50 short notes at the lower frequency
38594 CALL 38601 Check whether ENTER, 0 or the fire button is being pressed
38597 RET NZ Return (with the zero flag reset) if it is
38598 INC HL Move HL along to the next byte of tune data
38599 JR 38562 Jump back to play the next batch of 100 short notes
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