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John Snape 2023-04-11 13:48:26 -07:00 committed by GitHub
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1 * The standard Apple II "Air-raid" bell has
2 * been replaced with a gentler tone. Use it
3 * to give users some aural feedback that
4 * they are using a ProDOS program.
5 * The code for it follows.
6 *
7 SPKR EQU $C030 ;this clicks the speaker
8 *
8000: 00 9 LENGTH DS 1 ;duration of tone
10 *
11 * This is the wait routine from the Monitor ROM.
12 *
8001: 38 13 WAIT SEC
8002: 48 14 WAIT2 PHA
8003: E9 01 15 WAIT3 SBC #1
8005: D0 FC 16 BNE WAIT3
8007: 68 17 PLA
8008: E9 01 18 SBC #1
800A: D0 F6 19 BNE WAIT2
800C: 60 20 RTS
21 *
22 * Generate a nice little tone
23 * Exits with Z-flag set (BEQ) for branching
24 * Destroys the contents of the accumulator
25 *
800D: A9 20 26 BELL LDA #$20 ;duration of tone
800F: 8D 00 80 27 STA LENGTH
8012: A9 02 28 BELL1 LDA #$2 ;short delay...click
8014: 20 01 80 29 JSR WAIT
8017: 8D 30 C0 30 STA SPKR
801A: A9 20 31 LDA #$20 ;long delay...click
801C: 20 01 80 32 JSR WAIT
801F: 8D 30 C0 33 STA SPKR
8022: CE 00 80 34 DEC LENGTH
8025: D0 EB 35 BNE BELL1 ;repeat LENGTH times
8027: 60 36 RTS
--End assembly, 40 bytes, Errors: 0