10 GRAPHICS 23
20 FOR X=0 TO 39
30 FOR I=0 TO 3
40 COLOR I
50 PLOT 4*X+I,O
60 DRAWTO 4*X+1,95
70 NEXT I
80 NEXT X
90 A=PEEK(712)
100 POKE 712,PEEK(710)
110 POKE 710,PEEK(709)
120 POKE 709,PEEK(708)
130 POKE 708,A