10 IF PEEK(&H10D)<&H80 THEN 440
20 EXEC &H6C00
30 ALL
40 ORG 490
50 @FLAG EQU $E6
60 @BUTTONS EQU $E7
70 @XPOS EQU $F8
80 @YPOS EQU $FA
90 @IRQVECT RMB 2
100 @START LDA #$18
110 STA $FF07
120 LDA #$1
130 STA $FF06
140 LDX $10D
150 STX @IRQVECT
160 LEAX @IRQ,PCR
170 STX $10D
180 LDA #0
190 STA @FLAG
200 RTS
210 @IRQ LDA $FF05
220 ANDA #8
230 BEQ @FIN
240 LDB $FF04
250 LDA @FLAG
260 BEQ @CTRL
270 DECA
280 STA @FLAG
290 ANDA #1
300 BEQ @YDIR
310 ADDB @XPOS
320 STB @XPOS
330 BRA @FIN
340 @YDIR ADDB @YPOS
350 STB @YPOS
360 BRA @FIN
370 @CTRL TSTB
380 BPL @FIN
390 STB @BUTTONS
400 LDA #4
410 STA @FLAG
420 @FIN JMP [@IRQVECT]
430 END @START
440 EXEC
450 PMODE 4,1:SCREEN 1,1:PCLS
460 IF (PEEK(&HE7) AND 1)=0 THEN PCLS
470 LINE-(PEEK(&HF8),255-PEEK(&HFA)),PSET
480 GOTO460