ca65 V2.17 - Git 582aa41
Main file   : duck_shoot.ca65
Current file: duck_shoot.ca65

000000r 1               ;
000000r 1               ; ACORN System 1 Applications: Duck Shoot
000000r 1               ;
000000r 1               ; From the Acorn System 1 User's Manual
000000r 1               ;
000000r 1               ; (Chris Oddy January 2022)
000000r 1               ;
000000r 1               ; entry point $0200
000000r 1               ;
000000r 1               		.setcpu			"6502"
000000r 1               		.listbytes		unlimited
000000r 1               ;
000000r 1               TIME	:=		$0E
000000r 1               DEDDCK	:=		$1C
000000r 1               DUCK	:=		$61
000000r 1               DISPLAY	:=		$FE0C		; scan the display
000000r 1               RESTART	:=		$FF04		; Monitor reentry point
000000r 1               ;
000000r 1               		.org			$0200
000200  1               ;
000200  1  A9 1F        BEGIN:	lda		#$1F		; single scan display routine
000202  1  85 0E        		sta		TIME
000204  1  A9 00        		lda		#$00		; clear the display
000206  1  A2 07        		ldx		#$07
000208  1  86 20        		stx		$20
00020A  1  95 10        CLEAR:	sta		$10,x
00020C  1  CA           		dex
00020D  1  10 FB        		bpl		CLEAR
00020F  1  A9 00        REMOVE:	lda		#$00		; take the old duck off
000211  1  A6 20        		ldx		$20
000213  1  95 10        		sta		$10,x
000215  1  A9 61        INSERT:	lda		#DUCK		; put new duck on
000217  1  CA           		dex					; in new position
000218  1  10 02        		bpl		OLDX		; but not over the end of the display
00021A  1  A2 07        		ldx		#$07
00021C  1  95 10        OLDX:	sta		$10,X
00021E  1  86 20        		stx		$20
000220  1  A2 0E        		ldx		#TIME		; display interval is set by the byte loaded into X
000222  1  20 0C FE     WAIT:	jsr		DISPLAY
000225  1  C5 20        		cmp		$20			; hit ?
000227  1  F0 05        		beq		HIT
000229  1  CA           		dex
00022A  1  D0 F6        		bne		WAIT
00022C  1  F0 E1        		beq		REMOVE		; finished wait time
00022E  1  A9 1C        HIT:	lda		#DEDDCK		; put in a dead duck
000230  1  A6 20        		ldx		$20
000232  1  95 10        		sta		$10,x
000234  1  A9 FF        		lda		#$FF
000236  1  85 0E        		sta		TIME
000238  1  20 0C FE     		jsr		DISPLAY		; test for continuation
00023B  1  90 C3        		bcc		BEGIN
00023D  1  4C 04 FF     		jmp		RESTART		; or back to the Monitor
00023D  1