10 CLT:CLV:A=#64:B=#65:C=#67:D=#68:E=0:F=0:S=512
20 L=0:R=0:gosub 110
99 goto 410
100 ' Set motor speed.
110 E=-R:F=-L
150 if E<0 then O=1 else O=2
160 if E=0 then O=0
170 O=O+(ABS(E)-5)<<2
180 if F<0 then P=1 else P=2
190 if F=0 then P=0
200 P=P+(ABS(F)-5)<<2
270 poke #700, 0, O, P
280 I=i2cw(A,#700,1,#701,1)
290 I=i2cw(B,#700,1,#702,1)
320 return
400 '
410 if IN(4)=0 goto 490
420 S=ANA(0)
430 if S<340 goto 460
440 if S<680 goto 470
450 goto 480
460 L=50:R=-50:gosub 110:goto 410
470 L=50:R=50:gosub 110:goto 410
480 L=-50:R=50:gosub 110:goto 410
490 L=25:R=-25:gosub 110:goto 410