16 ; iy is left with YMADDR
18 ld (iy+1), $f0 ; key on
21 ;halt ; wait for interrupt
23 ld b, a ; b: cur frame
24 ld a, (prev) ; a: prev frame
31 bit 7, a ; 0: play, 1: stop
34 ld (iy+1), 0 ; key off
36 .keyon: ld (iy), YM_OPER
37 ld (iy+1), $f0 ; key on
46 ld (iy), a ; select reg
50 ld (iy+1), a ; write reg