18 ; iy is left with YMADDR
20 ld (iy+1), $f0 ; key on
23 ;halt ; wait for interrupt
25 ld b, a ; b: cur frame
26 ld a, (prev) ; a: prev frame
33 bit 7, a ; 0: play, 1: stop
36 ld (iy+1), 0 ; key off
38 .keyon: ld (iy), YM_OPER
39 ld (iy+1), $f0 ; key on
48 ld (iy), a ; select reg
52 ld (iy+1), a ; write reg