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

000000r 1               ;
000000r 1               ; ACORN System 1 Applications: Minidisassembler
000000r 1               ;
000000r 1               ; From the Acorn Teletext Board Technical 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               MOD		:=		$00
000000r 1               COUNT	:=		$0E
000000r 1               CHATS	:=		$0300		; character to screen
000000r 1               RESTART	:=		$FF04		; Monitor renentry point
000000r 1               ;
000000r 1               		.org			$0200
000200  1               ;
000200  1  A9 18        MINDIS:	lda		#$18		; disassemble 25 lines
000202  1  85 0E        		sta		COUNT
000204  1  D8           		cld
000205  1  A9 0C        		lda		#$0C		; start with a formfeed
000207  1  20 00 03     		jsr		CHATS
00020A  1  A9 0D        MAIN:	lda		#$0D		; carriage return/linefeed for each line
00020C  1  20 00 03     		jsr		CHATS
00020F  1  A9 0A        		lda		#$0A
000211  1  20 00 03     		jsr		CHATS
000214  1  A5 01        		lda		MOD+1		; display current address
000216  1  20 5A 02     		jsr		SPBYTE
000219  1  A5 00        		lda		MOD
00021B  1  20 61 02     		jsr		BYTOUT
00021E  1  A0 00        		ldy		#$00
000220  1  A2 01        		ldx		#$01		; X will be the byte count of the opcode
000222  1  B9 00 00     		lda		MOD,y		; fetch opcode, find it’s no. of bytes
000225  1  C9 20        		cmp		#$20		; ‘jsr' is an anomaly and is done first
000227  1  F0 17        		beq		CBYTE
000229  1  29 9F        		and		#$9F
00022B  1  F0 15        		beq		ABYTE		; binary 0XX00000 is 1 byte
00022D  1  29 1D        		and		#$1D
00022F  1  C9 19        		cmp		#$19
000231  1  F0 0D        		beq		CBYTE		; binary XXX110X1 is 3 bytes
000233  1  29 0D        		and		#$0D
000235  1  C9 08        		cmp		#$08
000237  1  F0 09        		beq		ABYTE		; binary XXXXX0X0 (now) is 1 byte
000239  1  29 0C        		and		#$0C
00023B  1  C9 0C        		cmp		#$0C
00023D  1  F0 01        		beq		CBYTE		; binary XXXX11XX is 3 bytes
00023F  1  CA           		dex					; all others are 2 bytes
000240  1  E8           CBYTE:	inx
000241  1  E8           		inx
000242  1  A0 00        ABYTE:	ldy		#$00
000244  1  B9 00 00     		lda		MOD,y
000247  1  20 5A 02     		jsr		SPBYTE
00024A  1  E6 00        		inc		MOD			; increment the byte pointer
00024C  1  D0 02        		bne		NOINC
00024E  1  E6 01        		inc		MOD+1
000250  1  CA           NOINC:	dex					; print all bytes required
000251  1  D0 EF        		bne		ABYTE
000253  1  C6 0E        		dec		COUNT
000255  1  10 B3        		bpl		MAIN		; finished the 25 lines ?
000257  1  4C 04 FF     GETOUT:	jmp		RESTART
00025A  1  48           SPBYTE:	pha					; print a space and then the byte
00025B  1  A9 20        		lda		#$20
00025D  1  20 00 03     		jsr		CHATS
000260  1  68           		pla
000261  1  48           BYTOUT:	pha					; print a byte
000262  1  4A           		lsr		A
000263  1  4A           		lsr		A
000264  1  4A           		lsr		A
000265  1  4A           		lsr		A
000266  1  20 6A 02     		jsr		DIGOUT
000269  1  68           		pla
00026A  1  29 0F        DIGOUT:	and		#$0F		; print the bottom hex digit in A
00026C  1  09 30        		ora		#$30
00026E  1  C9 3A        		cmp		#$3A
000270  1  90 02        		bcc		PUT
000272  1  69 06        		adc		#$06
000274  1  4C 00 03     PUT:	jmp		CHATS
000274  1