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

000000r 1               ;
000000r 1               ; ACORN System 1 Applications: Metronome
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               REPEAT		:=		$0E
000000r 1               ADDR		:=		$0E22		; A Data direction register
000000r 1               DISPLAY		:=		$FE0C		; scan the display
000000r 1               WAIT		:=		$FECD		; 300baud wait time
000000r 1               ;
000000r 1               		.org			$0200
000200  1               ;
000200  1               PERIOD	:=		$20
000200  1               CLRPA6	:=		$0E06			; clear bit 6 of PIA
000200  1               SETPA6	:=		$0E16			; set bit 6 of PIA
000200  1               ;
000200  1  A9 1F        METRO:	lda		#$1F
000202  1  85 0E        		sta		REPEAT		; set display to single scan
000204  1  A9 40        PULSE:	lda		#$40
000206  1  8D 22 0E     		sta		ADDR		; define PA6 as output
000209  1  8D 16 0E     		sta		SETPA6		; use the INS8154 set bit mode
00020C  1  20 CD FE     		jsr		WAIT		; use the 300 baud wait
00020F  1  8D 06 0E     		sta		CLRPA6		; use the INS8154 clear bit mode
000212  1  A6 20        		ldx		PERIOD
000214  1  20 0C FE     DEL:	jsr		DISPLAY		; look at keyboard
000217  1  C9 16        		cmp		#$16		; up key ?
000219  1  D0 04        		bne		DOWN		; no
00021B  1  E6 20        		inc		PERIOD		; decrease PERIOD
00021D  1  B0 E5        		bcs		PULSE		; carry was set by the compare: always
00021F  1  C9 17        DOWN:	cmp		#$17		; down key ?
000221  1  D0 04        		bne		DELI		; no
000223  1  C6 20        		dec		PERIOD		; decrease PERIOD
000225  1  B0 DD        		bcs		PULSE		; carry was set by the compare: always
000227  1  A0 0C        DELI:	ldy		#$0C		; cycle time of u1/2 seconds
000229  1  20 CD FE     DELJ:	jsr		WAIT
00022C  1  88           		dey
00022D  1  10 FA        		bpl		DELJ
00022F  1  CA           		dex
000230  1  D0 E2        		bne		DEL
000232  1  F0 D0        		beq		PULSE		; end of this period so pulse
000232  1