17 ; iy is left with YMADDR
19 ld (iy+1), $f0 ; key on
22 ;halt ; wait for interrupt
24 ld b, a ; b: cur frame
25 ld a, (prev) ; a: prev frame
32 bit 7, a ; 0: play, 1: stop
35 ld (iy+1), 0 ; key off
37 .keyon: ld (iy), YM_OPER
38 ld (iy+1), $f0 ; key on
47 ld (iy), a ; select reg
51 ld (iy+1), a ; write reg