Commodore 64 smooth y scroller in BASIC

0 def fn y(p)=(peek(53265)and 240)or p
1 print chr$(147)
2 let m=7
3 let d=-1
4 poke 53280,peek(53281)
5 poke 53265,fn y(m)
6 poke 56334,peek(56334)and 254
7 let a$="EDCFRFCDEDCFRFCDEDCFRFCDEDCFRFCDEDCFRFCD"
8 wait 53265,128,80:print chr$(19); chr$(17); a$
9 let a$=right$(a$, 39)+left$(a$, 1)
10 wait 53265,128,80:poke 53265,fn y(m)
11 let m=m+d
12 if m=0 or m=7 then let d=-d
13 go to 8