# Chiptune [Courses](https://asm-editor.specy.app/learn/courses.md) › [Z80 assembly](https://asm-editor.specy.app/learn/courses/z80.md) › Examples Web page: https://asm-editor.specy.app/learn/courses/z80/examples/chiptune > Play a short tune on the MSX sound chip: two square-wave channels play the melody and bass, while noise and a volume envelope create the drums. The same program in: [M68K](https://asm-editor.specy.app/learn/courses/m68k/examples/chiptune.md), [MIPS](https://asm-editor.specy.app/learn/courses/mips/examples/chiptune.md), [RISC-V](https://asm-editor.specy.app/learn/courses/risc-v/examples/chiptune.md) This tune uses the **Sound chip**, the MSX's AY-3-8910: channel A plays the melody, channel B plays the bass and channel C plays the drums. Choose **Build**, then **Run**, with your sound on. The chip has three square-wave channels, one shared noise generator and one shared **envelope generator**, which changes volume over time. A volume value of 16 makes a channel follow the envelope. Here channel C uses shape 0: its volume falls from full volume to silence and stays there. Writing 0 to shape register 13 restarts that fall, striking the drum; even writing the same shape restarts it. Each `setup` line pairs a register number with its value. The initialization loop selects the register through port `0xA0`, then writes the value through `0xA1`. | Pair in `setup` | Purpose | | --------------- | --------------------------------------------------------------- | | `7, 0x9c` | Mixer: tones on A and B, noise on C | | `8, 11` | A's fixed volume: 11 | | `9, 14` | B's fixed volume: 14 | | `10, 0x10` | C follows the envelope (`0x10` is 16) | | `11, 0x58` | Low byte of the envelope period | | `12, 0x02` | High byte: together `0x0258`, or 600, for a fall of about 86 ms | A 0 bit in the mixer enables a source. In `0x9C` (`10011100`), bits 0 and 1 enable A's and B's tones; bit 5 enables C's noise. Bit 7 controls an unconnected I/O port and has no effect here. The noise period sets the drum's brightness: 24 gives a low thud, 6 a snare-like sound and 1 a bright hi-hat-like sound. Each step occupies five bytes. The first row, `.word 214, 854` followed by `.byte 24`, means: | Offset from `ix` | Value | Meaning | | ---------------- | ----- | --------------------------------------- | | 0–1 | 214 | A's tone period, low byte first | | 2–3 | 854 | B's tone period, low byte first | | 4 | 24 | Noise period; restart the drum envelope | A zero in either tone field leaves that channel unchanged. A zero drum byte means no new hit: any previous envelope fall continues. Neither kind of zero silences a channel immediately. ```z80 .org 0x8000 ld hl, setup ; pairs of a register and its value ld b, 6 init: ld a, (hl) out (0xa0), a ; select the register inc hl ld a, (hl) out (0xa1), a ; and write it inc hl djnz init ld ix, song step: ld l, (ix+0) ; the lead's period ld h, (ix+1) ld a, h and l inc a ; 0xFFFF ends the song jr z, done ld a, 0 ; registers 0 and 1: channel A's period call tone ld l, (ix+2) ; the bass's period ld h, (ix+3) ld a, 2 ; registers 2 and 3: channel B's period call tone ld a, (ix+4) ; the drum's noise period or a jr z, wait ; 0: no drum on this step ld c, a ld a, 6 ; register 6: the noise period out (0xa0), a ld a, c out (0xa1), a ld a, 13 ; register 13: the envelope's shape, out (0xa0), a xor a ; 0, falling once to silence: writing it strikes the drum out (0xa1), a wait: ld bc, 0x0f50 ; b = 15 hundredths of a second, c = the wait port in a, (c) ld de, 5 add ix, de ; the next row jr step done: ld bc, 0x3c50 ; let the last notes ring for 60 hundredths in a, (c) halt ; the program's end silences the chip ; Writes the period in hl to the registers a and a + 1, unless it is 0. tone: ld c, a ld a, h or l ret z ; 0 leaves the channel as it is ld a, c out (0xa0), a ld a, l out (0xa1), a ; the low byte ld a, c inc a out (0xa0), a ld a, h out (0xa1), a ; the high four bits ret setup: .byte 7, 0x9c ; mixer: tones on A and B, noise on C .byte 8, 11 ; channel A's volume .byte 9, 14 ; channel B's volume .byte 10, 0x10 ; channel C follows the envelope .byte 11, 0x58 ; the envelope's period, 600: about 86 ms to fall .byte 12, 0x02 ; One row a step, an eighth of a bar: the periods of the lead and the bass, then the drum's noise ; period. 0 leaves that channel as it is; a lead of 0xFFFF ends the song. song: .word 214, 854 .byte 24 .word 170, 0 .byte 0 .word 143, 0 .byte 1 .word 170, 0 .byte 0 .word 214, 854 .byte 6 .word 170, 0 .byte 0 .word 143, 0 .byte 1 .word 107, 0 .byte 0 .word 254, 1017 .byte 24 .word 214, 0 .byte 0 .word 170, 0 .byte 1 .word 214, 0 .byte 0 .word 254, 1017 .byte 6 .word 214, 0 .byte 0 .word 170, 0 .byte 1 .word 127, 0 .byte 0 .word 321, 1286 .byte 24 .word 254, 0 .byte 0 .word 214, 0 .byte 1 .word 254, 0 .byte 0 .word 321, 1286 .byte 6 .word 254, 0 .byte 0 .word 214, 0 .byte 1 .word 160, 0 .byte 0 .word 285, 1141 .byte 24 .word 226, 0 .byte 0 .word 191, 0 .byte 1 .word 226, 0 .byte 0 .word 285, 1141 .byte 6 .word 226, 0 .byte 0 .word 191, 0 .byte 1 .word 143, 0 .byte 0 .word 214, 854 .byte 24 .word 0xffff ``` The first 32 steps make four bars of eight steps each, over C, A minor, F and G. Each step waits 15 hundredths of a second through the wait port. A 33rd step returns to the opening C notes and strikes the drum. The following `0xFFFF` word ends the table; after another 60 hundredths, `halt` silences the chip. The tone period is `1,789,772.5 / (16 × frequency in Hz)`: 214 gives about 523 Hz, the C an octave above middle C, and the bass's 854 gives about 131 Hz. A larger period gives a lower note. At `step`, `and l` must produce `0xFF` for `inc a` to wrap to zero. This happens only when both bytes are `0xFF`, detecting the sentinel before reading the rest of a row. In `tone`, `h OR l` is zero only when the whole period is zero, so `ret z` skips the write. Adding 5 to `ix` advances to the next step. ## Try it Make the drums longer by editing `setup`: change `.byte 11, 0x58` to `.byte 11, 0x00`, and `.byte 12, 0x02` to `.byte 12, 0x04`. Change the values, keeping the register numbers 11 and 12. Period `0x0400`, or 1,024, gives a fall of about 146 ms. Keep those edits, then give the lead the envelope too: change `.byte 8, 11` to `.byte 8, 16` in `setup`. Each drum hit now restarts the same 146 ms volume fall for both the lead and the drums. A lead note alone does not restart it. On steps without a new hit, any unfinished fall continues briefly, then both channels stay silent until the next hit. The bass keeps its fixed volume. The [Sound chip ports](https://asm-editor.specy.app/documentation/z80/io/sound-chip.md) list the other registers. ## Instructions in this Lecture - Z80: [`ld`](https://asm-editor.specy.app/documentation/z80/instruction/ld.md), [`out`](https://asm-editor.specy.app/documentation/z80/instruction/out.md), [`inc`](https://asm-editor.specy.app/documentation/z80/instruction/inc.md), [`djnz`](https://asm-editor.specy.app/documentation/z80/instruction/djnz.md), [`and`](https://asm-editor.specy.app/documentation/z80/instruction/and.md), [`jr`](https://asm-editor.specy.app/documentation/z80/instruction/jr.md), [`call`](https://asm-editor.specy.app/documentation/z80/instruction/call.md), [`or`](https://asm-editor.specy.app/documentation/z80/instruction/or.md), [`xor`](https://asm-editor.specy.app/documentation/z80/instruction/xor.md), [`in`](https://asm-editor.specy.app/documentation/z80/instruction/in.md), [`add`](https://asm-editor.specy.app/documentation/z80/instruction/add.md), [`halt`](https://asm-editor.specy.app/documentation/z80/instruction/halt.md), [`ret`](https://asm-editor.specy.app/documentation/z80/instruction/ret.md) Previous: [Play a tune](https://asm-editor.specy.app/learn/courses/z80/examples/play-a-tune.md)